What is the easiest way to catch Heatran?

With a masterball?

Or for harder alternative, Dusk balls, they have 4x catch rate in caves and at nighttime anywhere

Basically:
Get a Swampert (water/ground types) so the take 25% of lava plume and 50% of his iron head attack

Use muddy water if his lv is good, it will get him nearly half health.
Use it again it should be red health.
Keep on using dusk balls (be ready for up to 200 uses because his catch rate is about 1/2, even lower than Giratina) But if you're lucky, it could take 50 or so.

Ok I caught it using my palkia and throwing dusk balls. Try a powerful Pokemon with false swipe and make sure you save before encountering it.

-Shadow Cresselia

Use a Master Ball.

I had to use a timer ball. But if you paralyzed him and used a dusk ball that might work. Easiest way though is with a masterball.

Well the easiest way is to toss a masterball at it. The smartest/easiest way is bring a whole bunch of pokes about his level and use not very effective moves against him until he has low life. Use false swipe if you must. Then either put him to sleep, or even better paralyze him. Then just go nuts with dusk balls and ultra balls. Theres nothing special you have to do to catch one Pokemon that you don't do to another. You should have figured that out by now, some are just tougher to catch then others.

The most easiest is a master ball.The other way is bring a Pokemon that can cause heatran statues problems like jolteon,pikachu/raichu(with thunderwave)and etc.then toss a dusk/ultra ball.If it doesn't, try timer ball.I caught mine with 10 ultra balls and 6-9 dusk balls.Rather than paralyze you can have it sleep/poison.Be careful if it faints.heatran can't be burn with an attack.only effectspore/flame body.