The Reapers are effectively the Death Star, but in Squid-Droid form. Really, you could take a Star Destroyer, remove shields and like most of the other stuff, and move the turbolasers to it's tentacles, then slap on a Death Star laser on it's spine, and make it a droid, and you're pretty good to go. The smaller ones can enter atmosphere, and are much smaller than the big ones, so maybe pick the Gladiator class star destroyer for them, and maybe go with the Super Star Destroyer for the regular reaper. Although, the smaller destroyer sized ones do still have a massive laser. Maybe it's not as powerful, and that's the difference. You might survive the destroyer size hit, if the big guy hits you, it's like the death star - nothing survives.