I have a slightly different problem from just experiencing bad/poor roasts/beans.
In the UK , I am mostly a soya latte drinker. The choice of soya milk can be the difference between a 'good', or even 'alright' coffee to OMG THAT IS VILE. Some smaller 'independents' use chiller soya milk which normally has a bit of vanilla or some other hideous flavour that overpowers everything, even a strong roast. I've been to many 'posh' coffee houses that have ruined amazing coffee with terrible soya milk. Why they think this is a good idea I have no comprehension....probably because they don't drink soya lattes themselves. A lot of the 'main' chains like Starbucks, Nero etc use the Alpro professional which is sweetened slightly with apple juice to give a similar sweetness to normal milk. I tolerate it, but by far the best soya lattes are those made with unsweetened soya milk. Organic hipster cafes often use unsweetened, as do (funnily enough) both Waitrose and Sainsbury in their supermarket cafes. I am not a snob and will happily snap up a Sainsbury coffee if there is one in the vicinity of wherever I am working. Probably the best widely available soya lattes.
The best espresso I have ever had was outside a mechanics garage in Pila, Italy. Lavazza, but not like I had ever experienced in the UK. It was amazing. I'll never forget it. It put the French espresso I had been drinking for the 7 days previous to absolute shame.