Advice

I would like some advice on my game,

I tend to lose games to lower rated players more than higher rated players, and i am not sure why....Its the way they play lines out of my comfort zone, which are wrong but i never know how to punish them. 

I find solving puzzles helps, but it only helps to an extent, the ability to visualise why a move is wrong will probably take a lot of experience. 

I also wanted some advice on choosing an opening repertoire, I always mix things up...whilst this is good for beginners to get an idea of all the openings, I would like to choose one or two but dont know which one to pick....I hate playing against the ruy lopez, so maybe il pick that, or kings gambit, which is so tactically difficult to face. What are some of your opening repertoires?