Not being familiar with either game, I'll go off what I'd generally prefer according to what I remember of the Rogue Squadron novels. So none of the above. I'd go with improved engines. That's the Interceptor's schtick: sheer speed. It's a zoomy little beast. Smaller wings, so harder to see, and stupidly fast/maneuverable. So I'd be highly tempted to go with becoming even more stupidly fast and doubling down on what it's already good at.
By game logic, I'd have to ask what the overall missions are going to be. If it's dogfights, I'm sticking with speed or (in a close second) shields so one X-Wing blast doesn't take the TIE out. If it's taking out capital ships, a torpedo/missile launcher might be more useful.
Honestly, if it's a mix of missions, I'd be looking to get new ships as quick as possible. Advanced X1s are a more multi-role ship, so instead of being really good at one thing, they're pretty good at multiple things.
If it was me playing, though, I'd be talking about raiding Chiss space to steal some Clawcraft. Or I'd be on the lookout for TIE Defenders, because might as well shoot for something awesome.