So, I've been thinking of making a portal mod, but I don't know which game in the series I should mod. Should I mod Portal 1 or Portal 2?

IF you r planning to use any I.A at all (walking npc's and combat in an oversimplification) better stick to p1 but p1 is a bit more harder to work with imo, if you want better visuals more test elements and don't care much in not having Hl2 I.A features in your mod, go P2.

Either one you choose, i think you should not jump straight into a mod production if you r just starting in modding, better do some workshop mappacks and/or single maps first.

Okay, thanks for the reply!