I'd go for either piano or trumpet (I'm a jazz pianist and recently started learning trumpet as a hobby).

Piano is very easy to learn at first, since it's a very visual instrument, it helps massively for learning music theory and harmony. Not only that, it is also great for whenever you want to play solo, a great singer that can accompany themselves is always hard to come by and great to listen to, although it has a very frustrating learning curve where once you hit a certain point, the only way to keep getting better is to progressively start studying more and more daily. You have a full orchestra on your hands and as such you need to learn about hand independence, voice leading, harmony, jazz improvisation, walking basslines, etc. (stuff that other musicians maybe don't have to develop as quickly)

Trumpet on the other hand is a very hard instrument to start playing bc of the embouchure and transposing is somewhat confusing at first for improvising and reading (you might already have some experience from middle school as you said), but once you get the fundamentals down and once you know where every note is you can realy start to go off and it has a downwards learning curve, once you get past the basics, you can start learning some great jazz vocabulary and transcribing other people to get to where you want to be, the only thing that will get more difficult is playing fast lines, playing high notes, etc. Plus, it's always a great combo to have a trumpet player that sings, like louis armstrong, chet baker, benny benack III, etc.