buying a skin

I am looking for feed back on skin purchase. Thses champs and I play them a lot and do well with. Rengar who I just got in a box, kha'zix and I have his mecha skin which is ok but like his new one, or J4. J4 plain skin drive me bonkers. So tacky but never seen any of his in game. Rengar is on sale. What would you suggest. Thank you