what heroes is this spell mandatory? what heroes take this spell because other spells arnt that great for them?

lately, i find myself choosing teleport less and less. i find the better i get at the game, the less i need it.

I like it on strong physical carries or AOE characters who can push a tower quickly. You can let a creep wave ride and then teleport to attack or defend quickly with it. I also like it if there is a Teemo on our team since you can teleport to any mushroom.

Teleport is probably one of the best summoner spells in the game overall, but I don't know if it's mandatory for anyone really. It just depends on how well you can farm and control lanes with your character. Champions that need to go back to shop/heal a lot, champions that need extra assistance controlling lanes, or champions that are relatively slow getting around places are generally the ones who pack t-port.

Most useful champion I can think of are:

Ashe - Fire ultimate and teleport to where it will hit.

Kassadin - Bounce around using ultimate to build up 'charges' while your mana is being refilled by your base fountain then teleport in and ulitmate on someone.

Heimerdinger/Shaco/Teemo - Can all make use of dropping something that they can teleport too i believe.

And then anyone that needs to hop lanes to push/defend can make use of it. Like Master Yi using it to backdoor.

I used to take it all the time, but I do so much less these days. Oddly, one champ that I would automatically take it on is Twisted, just to boost his agility to insane levels and save up a Gate cooldown.

With that one exception, I would suggest that it's best on slow heroes (duh). I first started not taking it on Cho'gath with Boots of Mobility, as the insane speed he got made me feel like I could comfortably swap for combat spells. Even then, there's no hard and fast rule. I play Tristana almost exclusively with Flash and either Exhaust or Ignite, depending on my mood; Flash is essential for my method of play, and the extra damage or debuff can make all the difference. Being a little slower in the field is an acceptable exchange.

Of course, there is the 'middle ground', Ghost. Shorter cooldown than teleport, and has some other applications.

Others have named some champs it's particularly good with (especially pushers for saving towers or knocking down enemy towers when the opportunity arises). But I find it's more about team composition. If the rest of my team isn't taking teleport, I might. If the rest of my team all have teleport, I'm far more likely to take another combat skill like Exhaust or Ignite, or even Clairvoyance or Fortify (spells it's nice to have on a team anyway).

If you are really thinking team-wide, though, I think you want ~2 teleports on the team, on support and pusher characters. You want your carries to take powerful spells for fighting, which teleport is not. Your solo mid Annie who wants to gank a lot will benefit more from Ignite or Exhaust, or maybe you throw Flash and Ghost on your physical carry for chasing. Or your carry is Teemo, who perhaps really wants Cleanse/Flash/Ghost for escaping (because he doesn't have a good escape ability otherwise) and Exhaust (since he has no stun, either). And Teemo is fast anyway, so why waste a slot on Teleport?

I don't think Teleport is essential on anyone, but it is essential to have on the team (especially if you don't have fortifies). You need some way to defend a distant tower from at least a mild attack.