what should i play?

Hi, im silver 5 at the moment but i can never get past the 50 lp since it look like after some wins im gonna get an unbalanced matchup with my team being outclassed by the enemy one until im back at 0 lp. (i get +15 to +17 a win and -19 to -22 a lose) One of my biggest problem with league is that i can never choose what to play since i always want the most optimal pick for me to get the most wins possible. I know too many champs, im decent with too much, i love too much of them and damn, i have a really hard time choosing my role and champ since when i play too much of one, i start getting worse with it (or maybe it's the bad team balance after winstreaks, dunno really) Currently what ive been trying is rotating roles after one lose (mid-top, top-jg, jg-adc, adc-sup) and use this site for choosing my picks : http://lolpickforme.com/ but well, i tend to get a winstreak and then a lose streak therafter like always. Pls, i need help!