I have a couple of requirements for favorite group. First, it has to be "relatively" affordable. Secondly for STI, it needs to be repairable (not just the temporary WD40 flush and pray).For STI, I prefer either 8 speed DA or 8 speed 600 (tricolor). Both can be had with dual pivot brakes, both are aesthetically pleasing, both are repairable (nine speed and higher are not), consumables (other than lever hoods, don't get me going on those!!!) are affordable as well. On my keeper STI road bikes, all have one of these two groups.On MTBs, the late 1980s Deore XT, like on my Cimarron, are great. Also great are the early 1990s Deore LX and XT. All are durable, function well, and are still affordable. Couple them up to the Tourney 7 speed push button shifters ($15 on Amazon includes both shifters, housings and cables), and you are good to go. OF course, the Deore thumbies are great too.On pre-STI road bikes, I like first generation Cyclone and late 1980s Superbe Pro. Unfortunately, both are starting to get pricey. On bar ends, the Suntour friction units are great, also increasing in price unfortunately.