PCE Kyukuoku wins. No competition. The NES version of Twin Cobra is surprisingly good. I haven't played the Genesis version much, but I just don't care for it. The graphics seem kind of stretched horizontally, and it feels a LOT harder (even on the easy level settings). I know Classic Game Room did a Youtube review of the Genesis version where it was overall praised, but I'll stick with the PCE version.
This game is pretty hard on all consoles. I think on the PCE version I've only been able to make it 5 or 6 levels in, and that's on a good day. The first level is really hard and took me awhile to beat. Then it's a bit easier, because you've got a nicely powered up weapon. But there's still a fair amount of level memorization. Lots of enemies not only shoot at you, but also will fly right into you. And you have to be patient when selecting the powerups since they have an erratic motion around the screen. It's challenging, but once you learn how to play it never feels too cheap.
For cleaning games, I usually use vinegar for the contacts. I know it's frowned upon, but it works so much better than rubbing alcohol, in my experience. Rubbing Alcohol and/or GooGone for the cases. The PS1 Nectaris I just picked up has permanent marker scribbled on the disc.
I'm not too sure if I should even attempt cleaning that off.
