I started with X, Mario-style or whatever, but quickly shifted to RT after like level six. 
 
NEVER NOT RUNNING.

I thought you could only use X. Okay, I'm switching to RT.

Right trigger all the way.

Right Trigger until my finger starts to hurt then i switch to Left Trigger. Mainly RT though.

x all the way!
you gotta kick it old school.

X through all the light levels and like 40% of the dark levels so far.
I tried LT for a bit and that seems fine too.

"NEVER NOT RUNNING. "

X and always running!

" X and always running! "

" I thought you could only use X. Okay, I'm switching to RT. "

" @TheGreatGuero said:

" I thought you could only use X. Okay, I'm switching to RT. "

This. My aching thumb is saved! "

I started playing with my Mad Catz fight stick, it was amazing how much tighter the controls got.  If you have an arcade stick, try it for this game for sure.

Grew up using X button, seems most comfortable to me now.  Is anyone else starting to get Street Fighter IV-esque calluses on their run/jumping thumb?

" NEVER NOT RUNNING. "

I also didn't realize you could use the triggers.  Grew up holding down run and mashing jump with my thumb joint since SMB, so I just naturally fell into it.

I'm definitely going to give RT a try though.

I tried using my MadCatz Fightpad, but the button placement was awkward.  Perhaps with the trigger for run it won't be so much.

I feel like I have more accurate control with the X for some reason but if it is a never not running level I switch to LT after 10 or so deaths.  Even then though I still hit the A button with my thumb knuckle.

Always RT.  Although after about an hour of play I need to take a break 'cause my finger (actually, my whole body from my muscles being so tense during play) hurt.  
 
And, yes, @takua108 said:

"NEVER NOT RUNNING. "

I don't play it, but as I automatically hold x when playing sidescrollers no matter what, I can imagine that that would be my button of choice.
 
@Dany said:

" @dankempster said:

" @TheGreatGuero said:

" I thought you could only use X. Okay, I'm switching to RT. "

This. My aching thumb is saved! "

Your index finger will hate you for this. "

Didn't even know you could not use Rt. I'm still sticking with it, so I can run and jump easily.

Didn't know about X to run for the first three worlds so I'm in the habit of using RT. Pretty uncomfortable but feels right.

" I thought you could only use X. Okay, I'm switching to RT. "

Right Trigger, my thumb takes a little longer to go numb this way.

You can use LT? You probably just saved me from being forefinger invalid!

I didn't even know you could use LT.
 
I use the Right Trigger.  I tried X for a bit, since that's how you had to play most old school platformers, but trying to use your thumb to do two things at once means one of those things is less precise, at least for me. 
 
I haven't had any trouble with my fingers getting worn out, but because the levels are so short (30 seconds at most, so far), it is a great game to play a few levels here and there, so I've been using it as a palette cleanser.  I'll play for 15 minutes, then play another game for a while (Oblivion, lately.  Seriously, I bought that game when I got my 360, and I am only finally close to beating it, 3 years later)

I've been using X, I had no idea about RT. I shall try that out.

Right Trigger, because using X makes you hold the controller in a retarded manner.

I've only used X, being fairly use to using my thumb to hit two buttons at once. It's not nearly as bad as having to crab claw some virtual console titles with the gamecube controller.

YOU CAN USE THE TRIGGERS! Fucking shitcunts, I've been using X for 6 worlds now.

Definitely RT. I was using X but then I found it awkward to hit A and hold X while letting go of A at the right time for certain, more difficult jumps. Generally, RT is just more comfortable and easier.

RT; you want your run button far away from your jump button lest you accidentally press one or the other.

Right trigger! Had no idea you could use x.

I mostly just use the X button because of my mario super thumbs, but if i've committed to a level and i wont stop until its done i change between X and RT to give my thumb a rest.

I pressed the Left Trigger button on the poll, but I actually use RT. I guess I just ruined the truthiness of this poll.  
 
Sorry, everyone!

I alternate to avoid my thumb from cramping like in the NES days.

X. So much easier than using the trigger buttons

RT
 
NEVER NOT RUNNING!!!!

It's more fun using X (old school like) but sometimes have to switch to RT to avoid twisting my thumb in unnatural ways when jumping alot

Oh noo. I clicked Left Trigger bymistake. 
 
Roscoe all the way, man!