Do both if both are offered. Do both if it's just to train. Do no-gi if you're going into no-gi comps. Do gi if you're going into gi comps. It's better to train with the comp you're entering in mind than to train with a tool you can't use in said competition. If you are going into NAGAs and Mundials, train w/ the gi. ADCC and MMA, no-gi.
Do both, definitely. It just opens up options if you want to compete later down the line, in gi and no-gi/mma competition.
I started out doing no-gi in a small school that didn't teach gi, got to a similar standard as my training partners within 6 months and decided i needed to move on. Found a Gracie Barra school where they offer both and i'm right back at the bottom. The guys that do both have much better positioning, awareness, submission setups and the rest.
I've since decided to start gi myself twice per week and i've been setting up armbars and triangles for fun. The gi really allows you to drill the moves into your muscle memory before making the transition, not to mention the added awareness and positioning required to defend against submissions.
I'm going to do at least 2 classes of each per week from now on
depends on your goals. personally i say do whatever you have more fun with. personally i have fun with both.