I have issues with topside and the triangle escape (I tend to just smack people in the face because I do MMA, but when it's straight grappling, I'm in a world of hurt).
The important thing is to posture first, and don't let them put your arm across. If they don't have your arm across AND you are posturing up, it's almost impossible for them to choke you out. If they don't switch to an arm bar or something and keep going for the choke, I would suggest circling towards whatever side your untrapped arm is at, this will loosen the triangle and usually break it, allowing you to pass. You can also try to stack while circling, but watch out for them to hook your leg and either sweep or try and tighten the triangle. When in doubt though, pick them up and slam 'em(if it's MMA).