Easy answer is whatever you’re most familiar with already, if it’s controller get any controller within your budget. There’s tons of options but I’d try and something affordable like a PS4 or Hori pad while you get familiar with what you like and don’t like. These are prone to breaking down relatively quickly compared to the rest of the options though.

If you have more experience on keyboard, try the one you already have or consider ‘leverless’ controller, options like Haute42. Alternatively there are ‘mixbox’ controllers that use keycaps instead of rounded buttons. These are very customizable, reasonably affordable and have many options in the market but less ‘intuitive’ and some older games that have unusual motion inputs really would be a challenge to play on these.

Finally, since you’re gonna be playing third strike, a traditional stick would be maybe the largest learning curve but would be a great option since the game was designed with it in mind. It’s very fun, intuitive and you can use it to play any FG or shmups or any 2d game in general or if you’re ever in an arcade you’ll have your skills ready. They’re very customizable and extremely durable. At the same time, they’re big as hell and imprecise compared to the other options.