With 18 years of democracy,who of these two parties should govern South Africa after the next election and will the voters ever get their heads out of the sand and at least vote with reason and principle rather than with sentimentality?  

In the DA's defence it can only be measured where it governed most, which is the Western Cape Provincial Government (WCPG) and its municipalities & the Midvaal Municipality. The ANC on the other hand has had almost the full layout of the land to be judged on.     

So how the two parties compare?   

1.The DA.
Since Helen Zille took over the reigns of governance in Cape Town from the ANC,the Western Cape had grown remarkably fast economically and otherwise in that it's GDP for Cape Town rose by more than 130% from the R116.6billion when the ANC controlled the Western Cape to R269billion in 2011. Prudent and thrifty management skills indeed.
The DA had managed to reduced the rate of unemployment in the Western Cape from 21.7% to just under 17%.Offcourse joblessness is still major issue as even the Cape does not create enough jobs for the locals, the DA Party has done very well for most Capetonians so far.
Service delivery in the entire Western Cape has risen to above the 15% mark compared to the rest of the country and Cape Town city debt levels have been reduced to under the R1billion mark since the DA took charge of the Province. So they spend wisely in the Western Cape and don't incur unnecessary debts or live beyond their means.
The DA has increased broadrange housing delivery annually to 7000 units,whereas the ANC could only managed to increase it to 3000 units annually in Cape Town when they were in charge. So more than double than what the ANC did. Even though housing is a provincial matter for Government and part and parcel of our Constitution rather than a local municipality matter,Helen Zille has still done more than she could for her constituents.
She has also raised the subsidies on the indigent database and ensured that electricity was supplied to informal settlements in and around Cape Town despite the fact that Eskom at time refused to supply electicity.Through portable sites, informal and semi-formal households were able to get the services they need. The DA has a budget in place for this and ensures that water,health care and sanitation are suitably cared for in the entire Province.
The DA is winning and they are growing in every community. Just last week in at the by-elections, the DA trumped the ANC by winning a hat trick seats which the ANC were defending. The ANC subsequently came out boasting in their press statements that these three seats would form the vanguard of its electoral recovery,and more so in the Western Cape. But the people of Kirkwood, Manenberg, Heideveld, Gugulethu and Grabouw all knew better and told the ANC to **** off.
2.The ANC.
Since the ANC came power in April 1994 how do their report card read in 2012:

South African Population in 1994: 40.4m / 2012 it's 50.6m

Per capita Gross Domestic Product in 1994: $5,600 / 2012 it's $10,700

Children in secondary education in 1994: 58 per cent / 2012 it's 72 per cent

Households classed as “formal dwellings” in 1994: 64 per cent/2012 it's 76 per cent

Homes with basic electricity in 1994: 58 per cent /2012 it's 81 per cent

Unemployment rate in 1994: 26 per cent/ 23.9 per cent

Share of total household income earned by black South Africans in 1994: 29 per cent/38 per cent in 2006

HIV/Aids prevalence among 15-49 year olds in 1994: 2.5 per cent /16.6 per cent in 2012 

Life expectancy at birth in 1996: 61.4 years  / 49.3 years in 2012

Maternal mortality rate per 100,000 live births in 1994: 150 / 625 in 2012

Murder rate per 100,000 people in 1994: 66.9 / 31.9 in 2012

Transparency International Corruption Perceptions Index in 1994 - 21st best in the world league/ 64th in 2012
Despite all these achievements, 40% of the population or 20 million South Africans still live below the national poverty line. The healthcare system was "modernise" in the early 2000's,yet the infant mortality rate is still six times higher than the OECD countries by comparison. 
Similarly, 5.5 million South Africans have HIV/AIDS or 10.6% of South Africa's total population and 17% of their adult population lives with this dreadful illness. On average in South Africa you would currently live 18 to 20 years less than someone somewhere else the same age as you that lives in another country. 
With constant outbreaks of bickering, infighting and tensions between themselves and their affiliates,the ANC party's showy display of unity and "democracy" is creaking fast and like a ticking time bomb its just waiting to explode. The ANC has become a state within a State and a law unto themselves in less than 20 years time at the helm.
Dan Sebabi, leader of Limpopo’s branch of Cosatu,says:"You have leaders in the ANC who are politicians by day and businessmen by night".
Gilbert Kganyago,the leader of Limpopo’s branch of the South African Communist Party,wrote:"We thought that South Africa could be different from the rest of the countries that came before us on the African continent. But at the rate that things are happening, we have actually caught up to the African scenario quite more quickly than we might have thought."
So far Helen Zille's DA has challenged the ANC government on a number of issues,including wanting to hold,mr Jacob Zuma, to a public debate on at least ten key issues. Poor people in South Africa, who are somewhat often under-educated and socially illiterate,had been far too easily swayed since 1994 to vote against their own interests. Driven by and too preoccupied with the ANC's Liberation tear shedding BS than anything else had all been so sentimental at best. The ANC have lost their moorings and their identification with the poor and the unprivileged,by their corruption,the taking of bribes, accusations that meet counter-accusations etc.And the DA should really capitalize on all that going forward.
Can the DA finally represent the interests of the poor and increasingly disenfranchised middle-classes in South Africa and win the next election? Who know's.In time most South Africans,black,white,coloured or indian might surely one day have identified themselves as DA supporters.
Most people in South Africa vote ANC,even though they identify and agree with the DA's position on matters. It's ignorance and misplaced loyalties that still make them vote ANC.The DA represents real values,not empty promises, as the Western Cape Municipalities have shown as they are the best run in the entire country.
The gap between the dominant ANC Party's perceptions of what is in South Africa's best interest and the sad realities of everyday life in South Africa is dangerously wide. The ANC is constantly perpetuating their power so as to not allow normal credible opposition parties like the DA to govern in their place.
The IMF estimated that it would take an annual growth rate of between 6% to 7% for South Africa to significantly reduce unemployment in the country's current state of 25.9%. Currently the ANC can only manage 3.4% as they don't know how to create more jobs for the locals and keep outsourcing jobs to India and suchlike countries. An inefficient job market and chronic lack of investment in infrastructure development and modernisation are the main factors behind this shortage of growth in South Africa. To much uncertainties that are caused by internal party divisions by the ANC are undermining South Africa's business climate and private investment into the country.