Normal

If I replay the game then I usually will go with hard

It depends. I play Resogun on Vet.... I have never played Ghost Recon on anything other than Vet. Kingdom Hearts is Hard as Hell on Hard and I would never play Critical.

I play on hardest difficulty or else most games are too easy outside of puzzles

Usually normal. I'm not into going all pro in gaming. I completed Halo Reach and ODST on legendary, and I think that was enough for me.

Depends Halo 1,2,3,4, Reach, and Odst I completed on Legendary and Uncharted and The Last of Us on Crushing and Hard, but usually I play normal I want fun and not frustration, and im older now with less time.

I like to start on the hardest difficulty, but if I can sometimes I lower the difficulty (specially on RPG's)

Usually i go with normal first. Then hard/very hard. Depends on the game though.

I just go with the flow. If a game is too easy, I'll change the difficulty to the point that it feels like a challenge to me. In Fallout 4, the difficulty I generally play it at is very hard most of the time and on survival mode when I'm farming legendaries. In the witcher 3, I just use light armor and go for a glass cannon playstyle. If a game is too easy, I'll generally get bored of it quickly.

It varies with me. RPGs I go for normal so I can enjoy the story without getting frustrated at the difficulty of the game, while platformers I'll go for the hardest difficulty as they can be quite easy imo.

Usually normal, at times 1up if i am very interested, 1 down if i just want to rush through the experience.