All of those are fine, I think Garen is still pretty good and I still see him often. I can almost guarantee you wont be able to play Amumu due to him being banned every game. My only advice is to pick a few people and learn them extremely well.
When walking through the snow, please, for the love of god, DON'T PICK UP STRANGE CRYSTAL SHARDS!
Garen still viable, just not as spin2win as before
Sion ap or ad, both do well
Amumu, Shen very viable, as these guys can potentially carry teams if played well, but of course they're banned just about every game, Amumu more so than Shen. People seems to be hating on mumu, rammus, panth, and eve nowadays.
Caitlyn you better be damn sure you're good with her, and have a good team. She can't carry as hard as other options. Seems pretty popular atm because "omg snipah!", so whether you can actually choose her is up to when you get to pick. From experience most cait in ranked is pretty terribad around 1200 elo range (you start ranked at 1200), so if you see one most likely the game just became a 4v5.
Janna, Sona viable as support, but depend on team for winning, if you got a team of baddies no matter how hard you support you're not gonna win
Kassadin instagib people, keep mejai up and don't die. Getting 20 stacks in midgame's usually a good way to get a surrender out of the other team.
Swain viable, i've seen good swains completely dominate especially if you can land your snare well.
Kayle depending on team
Morde, Olaf most faceroll champs ever, people don't seem to know how to counter them
Master Yi, Sivir you'll either faceroll or do horribad depending on team comp. and your own skills