Note: These are merely personal preferences, your's can and probably do differ.
I am not a fan of bar end shifters. Choosing between them between them and downtube shifters I will choose downtube every time. Reasons?
1. They get bumped by my knees (not frequently, but always at a bad time)
2. To me they don't feel as crisp or precise.
3. For me, they aren't any easier to reach than downtube shifters. This is probably dependent on preferred handlebar height (I like mine pretty low so downtube shifters are at close to the same height as bar ends), How deep the drops are on the bars, frame size, and a bazillion other factors.
Given the choice between STI and either downtube or bat ends I will take STI everytime. To me they seem to offer the ease of use that barcons are supposed to offer, but don't. I find that I shift more often with STI and it seems to actually keep me pedaling more efficiently. Note that I am a recent convert and have been in the downtube camp until I used STI on a 10+ week tour this summer.