Overview

While focusing on champions you personally enjoy and have practiced a fair bit is generally the best way to pick champions, it's also wise to select champions that fit especially well with your team, deal well with key aspects of the enemy team, or have enough utility to fit into just about any composition.

In this guide I'll go over good champion choices in 3 different scenarios - Blind Pick (no knowledge of your opponent's champions or your own carry), Weak Early Game/Range Disadvantage (your carry is weak early game or your opponent has a significant range advantage over your lane), or Strong Early Game/Range Advantage.

Blind Pick

Thresh - bar none the best support in the game, Thresh brings a bit of everything to the table. He has decent harass and peel, with 3 of his abilities having different forms of crowd control to help lock down opponents. On top of this, he's one of only two champion in the game with a tool to reposition teammates instantly. Dark Passage makes him particularly deadly with carries that lack quick escapes over walls but have other uses, like Kog'Maw, Draven or Jinx. Thresh also fits particularly well in pick comps filled with assassins, as he can set up kills on priority targets or help pull your team out of a botched dive.

Thresh Runes and Masteries can vary greatly, as he benefits from AD, AP, HP, and resistances alike. The most common thresh builds feature a mix of HP, Cooldown reduction and resistances. Personally, maxing Cooldown reduction early in the game is a priority, as the lower the Cooldown for Death Sentence, the more likely an enemy will be caught out of position as a result.

Dr. Mundo - Not your typical support by any means, but there's few champions you'd rather have in laning phase than a good Dr. Mundo. Like other tank supports, you won't be easy to kill, and Dr. Mundo's poke and inherent health regen make him one of the best early game bullies; because of this, a strong lane bully marksman paired with Dr. Mundo, like Caitlyn or Lucian, can zone out nearly any opposing bot lane. As an added bonus, if you grab Dr. Mundo early in the pick phase you will likely give your Top Laner or Jungler a free counter pick (assuming the enemy then picks their top laner before your team).

I wrote a full guide on Support Mundo a few months ago, so if you're interested in knowing what kinds of Runes, Masteries, build orders and other tips I might have, you can check it out here: http://team-dignitas.net/articles/blogs/League-of-Legends/5005/The-Element-of-Suprise-Support-Mundo

Weak Early Game/Range Disadvantage

Braum - one of the tankiest champions in the game with decent harass, it's hard to punish the Heart of the Freljord whether with sustained poke or quick burst. A good Braum can soak up incredible amounts of damage for his carry while setting up strong harass through his long range q's and auto stun passive. Braum also serves as a great answer to supports that rely on single spells to land on priority targets, like Blitzcrank or Morgana, since Braum can simply jump in front of the carry and in most cases, soak up the followup damage without much concern.

I go as tanky as I possibly can early in the game with my Runes and Masteries, with flat Armor Marks and Quints, flat HP Seals, flat Magic Resist Glyphs and a full defense mastery page. The flat HP and resistances, coupled with Braum's immensely powerful early game make him a threat to be reckoned with from the the gate.

Nami - the runner-up for the title of the best overall support in the game, Nami's healing and peeling can make any carry's life a bit easier. Nami has deceptively great range, making her great at harassing, even while she's focused on healing. The movement speed buffs on your carry for every spell you cast is also incredibly helpful for your carry to position better or get out of sticky situations. Nami also fits in nearly every team composition, largely because her Tidal Wave serves as a fantastic tool for both engaging and disengaging team fights.

I prioritize movement speed on nami, so I run 3 Movement Speed Quints along with flat Armor Marks, flat HP seals, flat AP Glyphs and 9/0/21 Masteries, making sure to take every point in Fleet of Foot. The small bit of AP helps her sustain and harass enough to make a noticeable difference, which can often times be the determining point in a close skirmish. Cooldown Reduction is another must-have stat for Nami, as her lowest base Cooldown on any spell is 10 seconds.

Strong Early Game/Range Advantage

Leona - in many ways an opposite tank to Braum, instead of jumping to your carry and protecting them, Leona is all about locking an opponent in place. Having a gap closer, single target stun and a ranged aoe stun means even if your opponent burns Flash, there's still a good chance you can secure the kill. The only real downside to Leona (and one of the primary reasons you need a carry that has a lot of power on their own) is she'll often be doing little to peel for her carry in fights, and rather be focused on picking out priority targets.

Like Braum and Dr. Mundo, I also stack as much HP and resist as I can with Leona, taking the same Rune and Masteries. Leona's Zenith Blade throws her into what can easily be unfavorable positions (especially if your target Flashed away when you started the cast), so it's important to give yourself the best chance at being able to survive

Soraka - while Soraka's revamped kit can still help weak early game laners survive bad trades, she excels as a support that can amplify a lane bully's dominance. With Soraka's very low Cooldown on heal, she becomes the focus for most opponents - which can work in your favor when you're looking for opportunities for harass. The only way to really defeat Soraka is through quick burst, which is rare for bot lane opponents to get early in the game.

Soraka's biggest weakness in her new kit is the fact that healing an ally now costs her 10% of her max health. This means stacking HP on Soraka (which actually used to be quite strong) is now relatively meaningless, and the stats she'd most prefer are HP Regeneration and Resistances instead. Keeping this in mind, I run flat Armor Marks, scaling HP Regeneration Seals, flat Magic Resist Glyphs and 2 Movement Speed Quints and 1 flat Armor Quint. For masteries, I run a 0/15/15 page, again, focusing on HP Regeneration and Resistances as the primary focus.

Conclusion

In truth, there a lot of things you can factor in when choosing your champions, and there are significantly more choices than I presented in this article available. Likewise, simply because your lane has better synergy and/or an overall better matchup does not guarantee anything - anyone can make mistakes and lose even the most favorable matchups. That being said, often times your familiarity with a champion will be much more crucial than any strategy you can preemptively come up with - the only way to know what works best for you is to simply go out and try it out!