I agree with marco-polo. Budweiser Budvar over anything! :p
Gambrinus (the silver one) and Kozel are quite good bottled/canned. On tap, not so much.
Pilsner Urquell contains yeast so not my favorite but I guess folks who prefer the stronger/bitter taste will appreciate it.
Staropramen is cheap industrial shit so steer clear of it in any form!
Also, bear in mind that due to volume of beer-drinkers (and their preference) in Prague city center, most of the renown beer cellars use a system that kind of reminds me how jet fuel is stored in wings. A large vat inside of which there is sack with beer/fuel which deflates as it's pumped out. The reason being, they don't need to contaminate the beer with air to push it out and they can serve draft beer that is unpasteurized / unfiltered. Kinda like the difference between fresh milk vs long expiry date milk. So most beer you'll be served in the tourist locations will taste different than if you go to small bars on the outskirts of Prague or elsewhere in the country where they use the old-fashioned keg system.