I found either GFCEU or FCEUX to be pretty good NES emulators. If one is crashing, try the other, but neither has crashed for me so I'm not sure why you had a problem. Bsnes lagged for me as well, and I don't like it at all. There's one other one called "Mednafen", but the version for Ubuntu doesn't seem to have a GUI front-end so it's not really a good option either.
For Genesis, there's Gens-GS (not in the usual repositories, you'll have to enable getdeb games if it isn't already), or DGen. DGen is quite good, but it doesn't have a front-end GUI. You can search for and install "TkDGen" from sourceforge. It hasn't been updated in years, but it works fine for me. You do need to compile it from source, but once you do (the usual "./configure, make, make install"), you don't need to be in the tkdgen directory to run it.