my picks for bans come from the following: shen, morganna, kassadin, jayce, darius, malphite, alistar, regnar, blitz. depends on what im planning on playing since ill be first pick. usually 2 then one for me, so its usually blitz, shen, morganna, alistar, then one for me depending on what the other team bans as well.

Blitzcrank
Alistar
Shen

Amumu, ali, shen, blitz, and ezreal

ez,karthus,ali,malph,shen,blitz,morg,amumu,jayce

Darius is too easily countered by kayle top, morgana is a nusence late game but her early game is very suseptable to ganks + burst. A strong talon will shut her down. Lee sin isn't OP but will be quite difficult if you are not well versed at fighting him, and/or your opponent is exceptional on him. No comment on ww.

My suggestion is, ban whom is strong aganst your perticular team. Have champs in mind, counter pick what you can, ALWAYS chose what you are more skilled at unless it is hard countered by the enemy team, or their counter isn't open to pick (but also be good at him. Countering somone is useless unless you are good at that counter.)