Robin 2160 - I only ever go for aeros so it's simple - half tanks means I've got loads of reserce and am in W&B, assuming no fatso friend, who besides which would be excused FO duty at the "controls full and free" check :-)
I do it by eye on the walk round and then see if the guage tallies.
Thankfully the 2160 guage seems to have some vague resemblence to reality, unlike the PA-28s I trained on which always seemed to be either momentarily full, but otherwise empty. There's a few other gizmos on the 2160 (warning light, fuel flow meter on the injected one that I fly) that all seem to agree with each other.