Not a fan of either.

Mystery Dungeon is far too boring for the gameplay. Takes forever to complete a dungeon and after about 6 floors, they start feeling repetitive as anything. The stories are good so I'd rather watch a walkthrough of it than play it myself. I powersaved my SMD to have Mew & Mewtwo as the team but still didnt get past like the 2nd dungeon. Got about half way (?) through GTI I think; the icy cavern area with Kyurem?
I had one Ranger game when I was younger. Don't have it anymore, and wasn't a massive fan of it. It was fun for a short while tho. Probably wouldn't enjoy it now. Pokemon Snap still da best spin off

(Unless if Colosseum / XD count).