So ive never really done any speedrunning and am looking to get into it, what would be a decent game to start with?

Whichever one you prefer. It's best to start with a game you know well, but anyone works as long as it's speedrunable. If you want a recommendation from me, I'd say Hollow Knight. It's fun to Speedrun but tricky to perfect. If you wanna try that, you can, but I'd advise starting with something more simple first.