crowd control

Wreck and chain reaction. Phaselock something and your gun damage goes through the roof. When fighting immune bosses you phaselock the small mobs and blast the boss. Absolutely murders multi-hitbox bosses like Bnkr.

My current Siren build

Never, ever take cloud kill. It scales really badly and is worthless once you get to TVHM or even UVHM. Subsequence and Thoughtlock may sound good, but are very situational. E.g. phaselocking a badass enables you to hit his critspot, spread a lot of damage around via chain reaction and takes him out of the fight almost immediately AND starts your cooldown as soon as he's dead, With Subsequence your "phaselock orb" would bounce around and maybe do something useful, maybe it gets blocked by a fence, or maybe it just locks a target far away that you can't hit. Either way, your action skill wont start its cooldown before it has completely ran out.

And thoughtlock, well, you can't hurt thoughtlocked targets. And I'd rather have a dead badass when opening a fight than a thoughtlocked badass that does almost no damage to enemies for 10 seconds and may or may not cause the bunch to shoot him instead of me. Also increases your cooldown, so that's REAL bad.

Phaselock is a great offensive tool, both Thoughtlock and Subsequence are... kinda "meh" at best.

Blight Phoenix has the Cloud Kill problem of scaling really badly at higher levels, some people like to put one point into it to stagger enemies in melee range... but I tend to kill myself with it - it detonates barrels around you.

Ruin and converge for all your slagging needs. The flame/corrosion/electro dots on Ruins are suffering from the same scaling problem as all elemental things, but man, that auto-group-slag is worth every point in the tree.

tl;dr

Maya is awesome, CC will come naturally with only converge and a short cooldown and her DPS, especially with SMGs and Cat class mods, is crazy while phaselock is going. Sadly, her elemental skills are pretty bad at higher levels.

Oh, and she does all this while also being able to heal herself, her teammates and insta-rez across the field with her phaselock.