i've played with both and have been hooked on pyro since day one, it is literally the only trick i carry withme when i leave the house. its smaller and easier to do in my opinion. i think third degree was an attempt at reinventing the wheel that wasn't necessary. so you don't have to have a deck of cards....big deal, i've found it MUCH stronger in the presentation when they have a card. the whole point is that you're making their chosen card appear blistered on your thumb and you have such a HUGE array of things you can do from taking their card that they chose and lighting the corner and putting it out with your thumb and finger to have it blistered on your hand to numerous other forms of presentation...let your imagination go wild and don't settle for what comes in the package.
With third degree you have to fish with an index, pyro you can find your card on the gimmick in a fraction of the time. and seriously, there's nothing wrong with forcing the card. truly if you're repeating the trick as many times as you can with third degree you're shooting yourself in the foot. remember, you're "burning" yourself, how many times are you really going to be repeating this in a real situation. When i've done it in walk around or tradeshows I wait a LONG ass time, even though its killer, I wait almost like as sniper to bust it out and kick some ass with it.
other cool things I've done with my pyro gimmick is to take a pencil and scribble along the inside with teh lead. this gives you an almost ash like burn on the blister because the graphite is transferred. I also have a gimmick I made where I can have a small amount of lighter fluid transferred to my finger tips as i squeeze the imprint onto my fingers so i can actually have real fire on my finger tips, have somebody blow it out, and then bam right in their face is the blister. as you can probably tell, i'm a die hard pyro fan for life. nothign aganist palter personally or anything so please don't get me wrong, it just seems unnecessary to eliminate the deck...then why don't they think of a name or a word and have that appear blistered on you? To me its like if I were to come out with Panic but instead of four kings they turn into four jokers but then even better you don't need a gimmick because i sleeve the whole deck.
...ok bad example but its 8 am right now and i have no idea why i'm up. but, just my opinion so don't hate me if you dont' already