Yorick

There is no best solo top, its all about ****erpicking pretty much

I can absolutely destroy most top lanes with Skarner and Udyr.
Cho'Gath, Galio and Maokai are all really good safe picks for if you aren't sure if the other team has a jungler.
Renekton is good for zoning late game champions with a weak early game.
Urgot is just all around good for shutting down lanes, as is Yorik.
Akali is great if your lane opponent doesn't have much cc or ranged harass.
Nasus is good if you think you will get to farm all day, same with Irelia.
Olaf is unexpected and fairly good despite what people say, though he can be countered.
Teemo is pretty good against most solo tops, but is squishy.
Trundle does pretty well, but can get faceraped by magic so be careful with that one.

If wukong does well farming

I like wukong makes for fun with decoy, so many variations makes it hard to counter just need CDR

I don't play a large variety of Solo Tops, but I can talk about the two that I play:

Cho'gath: Cho is a really safe top laner. Leveled Rupture and Feral Scream allows you to easily both clear and last hit entire minion waves not allowing people to push against your tower. His passive allows him to heal and regen mana from last hitting allowing him to stay in lane and recover for harass fairly easily. He is one of the best solo top picks if the enemy team doesn't have a jungler.

Nasus: Nasus is one of those champs that if you're going to play needs to be in mid or solo top to truly shine. His passive lifesteal plus a regrowth pendant allow him to essentially ignore most harass while farming. Early game he is rather weak due to limited Q farming, and he cannot hold his own against two enemy champs nearly as well as other top picks such as Cho'gath as he has no range. Going top with Nasus and finding you have a Caitlyn and Blitzcrank waiting for you is a terrible feeling. Nasus is based entirely around his Q which grows stronger as you last hit with it. If you can farm it up to 200 in 15 or 400 in 30 then he is a terror. When playing Nasus in a 1v1 environment, try to last hit every minion in every wave with your Q.


Cho'gath: Skillshot Pick. Reliant on landing Rupture for initiating most jungle ganks. Good for 1v2

Nasus: Auto-Attack Pick. If you don't farm your Q you are deadweight on your team. In 1v1's almost impossible to force out of lane at any level. Beware of champs that inflict Grievous wounds.

Gragas

heals every time he uses an ability

Drunken rage gives him ~10% damage resistance and regens mana

good harassing and long range... body slam is basically flash but on a short c/d.

easy to farm with.

not many people play gragas but he's very good.

You want someone with great sustain (self explanatory) and you want someone tanky (so they wont get tower dived 2v1 when the jungle shows up)

So tanky with lots of sustain. Nasus is pretty dam solid there, so is Garen, Irelia, and Yorick.

My personal favorite is ChoGath though. His passive gives him unlimited hp and mana in lane, and at level 5 or so he can one shot a full creep wave with W. And he can't be ganked since he is tanky and has hard CC. You pretty much are able to outfarm anyone in the game with near 100% lane CS and zero reason to ever go back to base since your passive tops you off. I often don't go back to base until I take their tower, or I have the full 3000g to buy a RoA all at once.

What you all seem to be forgetting, AP Soraka wrecks 9/10 melee solo top players AND, if selected properly, the enemy team will assume she's support when picking counters.

Particularly viable vs Garen, Kong, Akali, Malph, Ramus, Jarv, Renek, Nas, Cho

and reasonably viable against others such as Talon, Maokai, Nids and Rumble

I would say Gangplank, Irelia and Urgot are some of the best picks for solo top. Gangplank has good farming capabilities with his Q, can escape ganks with his W and E, and helps team from across the map with his ult. Irelia is good at farming and is great against squishier targets. Urgot is fantastic against a carry, with his amazing harass, though his ult is always fantastic against anyone for ganks or for pulling them into the tower if they're overextending.