My Il2 set up is very heavily modded and most of my favorite planes to just fly around in are not stock planes. My current fave is the modded J7W1 Shinden canard (my version of which uses a P-63 flight model). I spend a lot of time "outside the cockpit" watching my planes fly past and do aerobatics, and the Shinden is a great-looking plane. I also enjoy tooling around in the Boeing P-26, F-86, Mig-15, Do-335, any of the I-16 series, any Spitfire, Me-262s, and the J8A (Gladiator) which has by far the most realistic-looking cockpit interior of them all.
When I actually go online to fight or set up combat sims, I usually limit myself to piston-engined stock planes that actually saw combat. Here, I would guess I prefer in order: Spits V and above, A6Ms, Ki-61/100s, Ki-84s, Bf-109Fs and above, F4U1.c's, Fw-190Ds and La5FNs and above. I tend to avoid all USAAF types except the P-38 because they lack cannon armament, and wont even think about Italian and early war JAAF types with their twin .303 pop guns. I also stay away from Fw-190As as I have never been successful in figuring out their wicked high-speed stalls.