It's a hard choice for me. 2 improved the gameplay but the horror aspects were seriously lacking compared to 1 (other than the Animus which was just as scary as anything in the first game). 2 was also a lot easier (I played Nightmare my first playthrough, and it felt like it was the equivalent of normal in 1, which is exactly what the devs said it would be so whatever). 1 had more memorable antagonists (Ruvik and Laura were great; Discount Hannibal in 2 was pretty good, and Theodore was lacking), better bosses, and better horror. 2 had better gameplay, better story, and better pacing.
Both are definitely worth playing, but in the end, it's a horror game. I play it to be terrified and 1 better delivered that aspect. Hopefully if they ever make 3, they throw out the open world and stick to carefully crafted and presented levels. Also, somewhat nerf the stealth. I think that's what made 2 such a cakewalk. You could stealth kill every enemy, and stealth your way out of most bosses. IMO some forced confrontation (at least for bosses) is important in a horror game. Otherwise, you feel too secure (which was the case in 2).