Keep the cables immaculate and the mechanisms free of old grease - they will all go click click click
1:1 actuation will feel snappier
'Shimano Total Integration' was pretty much sorted by 1995 so just about anything from Alivio up works very well.
Thumbies are just indented plates with a teeny tiny ball bearing all kept under load - keep this clean and they will feel like new forever-ver-ver-ver... But they dont make anyone any money.
Downtube levers put onto handlebar mounts are just terrible as they require further movement than a purposely designed thumbshifter.
Sachs Wavey were BRILLIANT!!!
Sram/ Gripshit were not.
Suntour Express shifters were just awful - I dont remember them being 8spd though.
Campagnolo Bullet shift was, erm, interesting
Modern SRAM uses a lot of plastic and can warp easily and is susceptible to bending or breaking under miss shifts