On Normal difficulty, a character with 60+ will and the Psi Armor has a very good chance to dominate anything organic that isn't an Ethereal or A Chrysalid even at full health.
Causing a few injuries (or preferably, using Mind Reave) significantly reduces their will and ratchets up your control success chance.
Mind-controlled enemies make ideal scouts, since absolutely nothing you care about gets hurt if they walk into an ambush. edit: Also, the enemy AI tends to prioritize by proximity, so they'll shoot your new "volunteer" first and give away their position.
Telekinetic field is /much/ more situational since it only lasts a very short time and requires proximity -- and Mutons and Floaters think "multiple XCom soldiers in proximity" rhymes with "Toss a grenade".
edit Downsides include:
Any aliens in your new 'volunteer forward scout's FoV trigger alert immediately; I've had one terror mission go south /really/ quickly when the muton I took control of could see three Chrysalids, a Floater spawn... and the Sectopod.
The alien gets control of itself back on its turn and you can't shoot it beforehand, so if you try to set it up for an ambush or stunbait, it gets a free shot back first.
This may be a bug, but your squad will get the "ally fallen in combat" willpower debuff if/when uncontrolled aliens blast your 'volunteer forward scout'. This has been fixed in a recent update.
Overall, I've gotten much more use out of mind control than TK field.