Favorite submission hold to finish with? Probably the Head-and-Arm choke aka Arm Triangle. A lot of guys just end up falling into position to get caught by this, whether they be standing, on top or on the bottom.
My favorite submission hold to work from is the Ude Garami (Judo: Entangled Armlock), aka "Americana/Keylock" in the overhead version or "Kimura" in the underarm version. Not only is this a great way to finish in general, but I've been able to set up Armbars, taking the back, the HAC, and even Kneebars (thank you Bas Rutten) by threatening this hold. It's probably one of the most versatile of offensive weapons when on the ground.
It doesn't matter if you agree or disagree
... As long as I don't bore you and I spark a moment of thought, my goal is achieved
Queng leon queng tigre ecu tacacut, queca pa? - Pampangan Mandarigma Motto