Best support and why? List reasons, builds, and build order.

Intelligent discussion please.

Depends. Who's your ADC? What are you against, both in lane and the enemy team as a whole? What holes need to be filled on your team?

At low elo/skill levels, Sona is probably the most versatile and easiest support available. At higher level, though, Janna and Lulu will win games with their ability to control fights.

LPF's got a point. It all depends on your ADC. More importantly, it depends on your ADC's playstyle. Lots of people like having a blitzcrank support them, since his kit allows for early kills. I don't like having a blitzcrank support me because I'd rather both my enemies and I sit back and farm. I'd prefer Taric supporting me. The stun to halt ganks, getting healed, extra armor. Day at the beach.

Not only does it depend on the ADC, it also depends on the person playing the ADC.

I was typing up a whole detailed explanation of the different type of supports based upon how the ADC plans to play, but I decided not to. In short.... Nami, Taric, Sona, Janna, and Alistar are probably the best choices to start with. They all have some sort of sustain (some requiring more skill than others) and some form of CC/ killing potential. Other champions depend more on specific play styles and match ups to win their lane and the game.

Sona support if you can find a good ADC MF, Ezreal, or Draven.
Good sustain op stun and a slow.
Zeke's Herald + Sonas Q passive +40 AD to ur adc and rest of ur team

There is no best, it is completely based on match-ups and players.

If you're still looking for a "best one", the closest we can get is Janna.

She was one of the champions that I earned the most ranked wins with in Season 2. Basically, Janna is in my opinion of the best because all her spells have an immense amount of utility.

First, her passive is one of the strongest in the game - 3% movement speed globally, for all allies! Seeing as 3% MS is worth 2 MS quints or 21 points into utility mastery, it should not be any wonder why this is insanely powerful.

She can push, disrupt, harass, peel, and chase with her tornadoes and zephyr, which is useful for the ADC in lane and generally the whole team later on. It gives you the ability to harass/push when needed, but also to help protect teammates or kill enemies. Even better, Zephyr gives extra MS while also making you ignore unit collision, which again, is very powerful. There are MANY times where this comes in handy, and one of the best things about Janna is she has such a speed advantage over everyone else, it allows you to do things you normally can't do, and makes it so much easier to plant wards. It makes it less punishing if you get caught out, or if you're far away from a teammate in need.

The shield is one of the best support abilities since it also doubles as an attack steroid. Then there's her ultimate, again a versatile skill. Can use it to push enemies away or towards team for initiates, peels, escapes, etc. Or, it can be used to heal a team to keep a push going, or give them enough health to take an objective like dragon.

Sure, she lacks a spammable heal, but I don't consider this a real weakness, and it certainly does not offset Janna's strengths. With the S3 changes, it has become easier for teammates to heal (Flask), and since pretty much everyone has some sort of anti-healing mechanism (Ignite, certain abilities/items), it's not a big deal.

Again, there is no best support, it all depends on the players and match-ups. However, Janna is one of the safest choices in the game.

I just need a support in general that adds the most throughout the game. one that I don't have to go aggressive with yet could if I wanted to. (so no melee attacking ranged only). I tried Janna a couple of times but I don't know if I just don't support good enough or my ADCs just sucked in general but I seem to fail with Janna, hard.

Lulu is a very powerful support. A shield, slow, damage boost. Not to mention her ultimate, which guarantees the survival of your carry, is great for initiating a fight on your diving bruiser or counter-initiating when someone gets caught - pretty much all amazing things to have in solo queue.

Personally I like Janna
Her passive is free movement speed for the whole team.
Her Q is and AoE knock up.
Her E is not only a shield but also practically a built in BF Sword.
Her W gives great movement speed and a decent slow to help keep the other ADC from getting away.
Her R a fight reset or with flash a blitz pull on steriods with a heal for lane sustain before roaming phase.

A far as build.
Philo stone
Boots of speed
Kages Lucky pick
Sightstone/Ionian Boots whichever one you want first
Aegis
-Situational Stuff-
Shurelya's Reverie
Ruby sightstone

Also I see you would like to be agressive or passive depending on the game.
Passive: Use your Q and E to protect the carry when they get attacked. Ulti to push the enemies away to protect the carries or to heal.
Aggressive: Use your Q to start a fight then shield then slow the enemy. Ulti to push one or 2 enemies into your team.