I like STI and think they are reliable enough, but... Given the choice between bar ends and downtube shifters I'll take downtube everytime. This is personal preference but my reasons are:
- I bump my knees on down barends and have unplanned shifts.
- Downtube shifters have cleaner simpler cable routing and shorter cables with less housing.
- I think downtube shifters are less prone to damage.
- Barends tend to get bumped when the bike is parked resulting in unexpected shifts as soon as you start riding.
- I have to take my hands from their normal position to use either.
- For my frame size and preferred bar height they are both at the same height, so no real difference in accessibility for either. Others who sit more upright, have higher bars, or have larger frames may find they have to bend less to use bar ends.
BTW: I would think any advantages for bar ends would also apply to the old stem mounted shifters that went out of fashion long ago. In fact it seems like they would have more advantages.
STI is just so much nicer to use that I don't see a reason to use anything else and am willing to accept the extra complexity and messier cable runs. I figure that if I break one on tour I will be able to use the other shifter for it's full range and pick one gear to use for the broken one (It can easily be jerry rigged to use any one in the ranges for either front or back). If a replacement isn't available I would pick up a downtube shifter at the next bike shop to use until I could replace the STI shifter. If on an extended tour in some third world country I would maybe carry a set of downtube shifters as spares.