Just How Much Better is ThunderBolt than Zap Cannon on Zapdos?

theyre on par. But 2 bar>1bar

http://pogomoves.com/check.php?lang=en&pkmn=Zapdos&basic=Charge+Beam&charge=Zap+Cannon

"Worth TMing" depends on how often you get them I guess. I'm lousy with them so I might answer yes.

In general though, no. Both moves are great and one could prefer one or the other for different reasons.

I have a 98% with Thunder. Should I TM that one?

Since this is the same problem: I have Thunderbolt 87% and Zap Cannon 96%. Who would you power up?
(Damn, I got lucky with Zappy...)

My 100% Zapdos knows Zap Cannon. I used it in battle yesterday for Lugia, and some regular gym battles. I have to say I hate it. It takes extremely long to inflict damage from when it is started. It is 140 power for 100 dust. Comparable to earthquake.

Thunderbolt is two bar and 80 power. So for the same 100 energy, you can use two, which comes out to 160. It is very fast and the animation time is very short. I always prefer using my thunderbolt Jolteons.

I will probably switch my 100% IV Zapdos to thunderbolt soon. All the others I have caught know zap cannon.