Top is all about what you. What I mean by that is you play different champions depends on the situation and what you feel comfortable with. Until you get up to the ~1400 area (silver 1) counter picks are kind of 50/50. Many times I have picked into a counter pick knowing I can play the champion better then my opponent is expecting.
That being said, Do not discount the counter pick. If I see someone pick a top garen. Your darn right I am going to go teemo. I know that no matter how well garen plays he has a distinct disadvantage.
So I will list some situations that apply to ranked/draft pick for solo top champs.
-The safety pick = you don't know what they are playing yet, but you know even if you are counter picked you can play to "not lose the lane" for me this is Vlad, Yorrick. I know that I can farm under my tower all game without worry of being ganked.
-Countering the team while being counter picked = Sometimes you need to do what the team needs. you see they have something that you don't trust the rest of your team to stop. (usually a katarina for me) so you being a middle pick decide to counter that person knowing full well you are going to get counter picked. This is probably the hardest situation. You know you've been countered and are going to have a real pain farming or surviving in lane. I can't tell you how many times I have been countered while playing riven. First off play safe, farm under the tower. balance the minion wave near your tower so you can get away. Don't follow the rule of "if they aren't in lane, push the lane." Last hit but dont last hit so much that it will cause the lane to push. If you get behind, cut your loses. 1 tower is worth 150 for everyone on their team, big deal. Letting a solo top snow ball is much worse. Ditch the lane. Help gank mid or bot with your jungle. Be useful else where if you can't safely farm. DO NOT FEED THAT COUNTER PICK. If that person is about equal skill level you "trying harder" is going to do much. Help your team get fed and let that top over extend. Gank him when he is out of position (on your side of river.) Play not to lose as much as you can, if you can't play to win somewhere else.
-The last pick! / the trade = You are getting the perfect pick! make the best of it! Take into account their team comp not just your lane. Pick so that you can not only counter top, but soft counter mid. That way if you have to you can lane swap. Play the champion you are best with that has an advantage over your opponent. Learn the counter picks! there is a ton of info out there on counter picking. Entire websites dedicated to it! (championselect.net)
other things to keep in mind
-runes/masteries = set them up per match or have a ton of rune pages and masteries (seriously i have like 15 pages of each)
-your build = Sometimes all in is not the best answer. if you can't live long enough to do anything. you aren't worth much.
-Checking your ego at the play button = Everyone will have issues with this one. It sucks to say but people are better then you. accept it, don't rage, do what you can, and LEARN FROM IT. You are not the best player out there, you won't always get your lane, and YES YOU WILL HAVE TO SUPPORT. But things I talked about apply to every single lane.
my top picks for solo top
-Kha Zix (know who I am against)
-Elise (they picked a bruiser)
-Teemo (lol silly garen)
-Lee Sin (they picked Akali/WK/Irelia)* Lee sin is also a safety pick if you are good with him
-Jayce (didn't see their pick wanted to play it safe)
-Vlad (counter AD or they lack sustain)* safety pick
-Warwick (They lack sustain, my team needed tank)
-Zed (Counter aggressive lane)
-Yorrick (really who even beats him in top?)
-Cho (good against Yorrick, good team pick)
-Malph (Counter ALL AD, if he isn't banned I am picking him)
There are a ton of other top lane champs, but those are some pretty good ones to at least have an understanding of them.