The only accurate stealth mechanic is to have the stealthed opponent map their movement separately where the opponent cannot see. But this is wildly impractical for many reasons, and I think I've only seen it used once, though I can't recall the game (hexes were involved) …
A good approximation systems I like, even if a bit too random, is from TREK ATTACK WING (and a variation is in X-Wing) of all things. Cloaked ships are still on the board BUT:
-- All Shooting grants them 4 extra Defense dice
-- When they decloak, they can reveal to be a small template away in directions chosen by the opponent.
The former works well on average, but if you're like me, I whiff all the defense rolls and it meant nothing. A more static auto-dodge token or two PLUS extra dice would work better.
The latter works AMAZINGLY well, giving that "Surprise, I'm over here!" effect when executed well. Doubly so for those effect that allow extended templates for the reveal displacement. For poor pilots though, they can easily be outmaneuvered into a wide front firing arc.
Worst "Stealth and Cloak" effects? The Relthoza in Firestorm Armada. First off, I can never keep straight which was which … don't give things similar names but wildly different mechanics. Second, the "Always On" effect was worthless because it nuked your own firepower OR simply made the game all about long range sniping for VPs then hiding - a terrible play experience for both IMHO.
Ironically PLANETFALL had the best system in that core mechanic - where reliance on "exploding" dice was crucial, simply taking that away for shooting at Relthoza had an amazing swing on shooting. I vastly preferred it over playing shielded forces.
