In terms of 1CCing from easiest to hardest.
1. Fighting games-These games are pretty much designed for 1CC. Whenever you lose a round or none, they are designed with it in mind as sometimes you can only get credits by doing a 1CC. Relying on skill and other kinds of tactics to win, it's almost always possible to 1CC a fighting game. Note that many are between 20-30 minutes with many even under 20 minutes as well.
2. Shoot em ups-This is a hardcore genre, but one that mainly focuses on memorization more than anything. There's lots of skill involved, but they are also designed to be 1CC as once you memorized pretty much everything and have good reflexes you can 1CC them. They tend to have extra lives, sometimes an overpowered weapon that can get you through the game faster, and are pretty much always built for 1CC. These games tend to be 20-30 minutes as well so that makes it better.
3. Beat em ups-For some reason I have the most trouble with this genre. I have 1CC beat em ups, but a lot of them are tough. This is due to them being designed to take away quarters more than anything else. I mean, a lot can be 1CC, but usually you have to do crowd control and rely on insane tactics to get anywhere. It doesn't help that various ones don't have extra lives, they often start you with 2 lives or even 1 life for some odd reason(should be 3) and have annoying enemies and bosses they tend to be cheap or pretty powerful to drain your health in a few hits. This genre to me is one of the most frustrating ones due to the fact that pretty much everything has to go your way in order to 1CC them, though it's fun to do still at least. It also doesn't help that they are usually between 40 minutes to over an hour long, and even 1 hour and 30 minutes at times.
Many Neo Geo games are fighting games, so 1CC is doable for practically all of them.
Also when it comes to putting in continues, only rely on single digit numbers, double digits is pretty much credit feeding at that point.=p