I fly the USAAF birds and the F6F without combat trim. Almost all of the others, I fly with combat trim--especially the Spits and 109s.
For me, I've pretty much got my controls optimized for flying P-47s, so I have rudder trim and pitch trim mapped to a hat on my throttle. Aileron trim stays on the keyboard because I'm out of hat switches, and the Jug is pretty stable in the roll axis, regardless of configuration changes. Most of the time, I have it trimmed for around 300 mph IAS "hands off". It doesn't seem to fight me too much at that setting, and when I pull through the vertical, I don't have to worry about it not being nose-heavy. The P-38 is particularly suited for manual trim, since there's basically no or little yaw or roll inputs to counteract.