I've ridden with down tubes, bar ends and brifters (I hate that word, but there is no other generic term for the STI/Ergopower shifters).
The only thing I miss about down tube shifters were their simplicity. When indexing started to become common in the mid-late 80's, I could never quite get used to it so I tended to run them in friction mode. Didn't have a bunch of springs and lever to mess with. You had that screw that doubled as the index/friction mode on the right side.
When I made the jump to STI in 1992, I fell in love with it. One of my physics professors in college said he didn't see what all the commotion was about, but he made the change to find out for himself. As it turns out, he found he was shifting more.
I've never been a huge fan of bar ends. My big complaint is that I tended to hit my knees on the things which hurt and frequently put me in a gear I didn't want to be in.
But, a lot of the rando riders like them (down tubes or bar cons) because of their simplicity. If a brifter breaks down 500km into 600km ride, you had better be able to fix it yourself or accept the DQ for getting it fixed somewhere.
Personally, I'm a big fan of Ergopower. They use a different mechanism than STI (neither of which I understand). They have a crisper feel and more trim than STI. And you can completely rebuild Ergopower shifters which is not the case with shimano.
However, with that all said, if you switch to Ergopower, you had best plan on using a Campy cassette. I have Phil Wood hubs which aren't compatible with Campy cassettes. The spacing on the Ultegra 10 speed cassette is similar but not identical to Campy so while it works, it's not quite right. My wife's drive train is all Campy and her shifting is much crisper than mine.
Here's why that is an issue. Shimano's widest range 10 speed cassette is a 12-27. Personally, I'd like a 12-30 but I take what I can get.
re-cur-sion ri'-ker-shen n: see recursion