It's good fun to fly on prop planes, or smaller types. I do actively seek these out where I can. You may have missed the Jetstream 31/32 on Sun Air now as it seems to be being withdrawn, but that's a great experience. As others have mentioned the D328 jet is a lovely machine, very fast climbing, also on Sun Air. Then a Saab 2000 LCY to IOM to complete the set (I think) in BA livery. I think you also have ATRs on Finnair via Wideroe, certainly I did one of these plus a Dash 8 on a Finnair routing last month but on Air Baltic.
You can certainly fly on a tiny Cessna on an AA ticket, but sadly not attracting TPs under the "operated by third party" rule.