That is a big piece of pie. I'll have to check Serious Pizza out. I went to a pizza place in Toronto once that had some huge slices, but I don't think they were that big.
In Dallas:
-I live near Bishop Arts District and really like Eno's pizza; dig the

thin crust and locally procured ingredients. I usually get a pizza with chicken, raw jalapenos (instead of the pickled, jarred variety, but cooked on the pizza), and feta cheese (in addition to the mozzarella). Nice beer and wine selection, too.
-Cane Rosso is good, not great. I'd put it on par with Coal Vines.
-I've heard good things about Olivetti's, but have never been.
-I really like Fireside Pies pizza, but don't like the wait most nights and am not sure the pizza is worth the premium price.
-For "bang for your buck", I think it's tough to beat Louie's on Henderson.
-If you like cheese, cheese, and more cheese, Piggie Pies is pretty tasty.
-Was shopping at NorthPark over the weekend and stopped into Grimaldi's across 75. Pretty good pizza for a chain.
-Campisi's is an institution and still makes a mean pie.
In OKC:
-I don't recall really having a favorite, but Pizza House at NW 25th and Penn, right by OCU, was damn good as recently as the early aughts.
-This sounds weird, but I kind of miss having Mazzio's as an option. Good, solid pizza at a fair price. Haven't had any in a decade, so it's possible its quality has gone down
Random:
-They still have a Crystal's Pizza in Irving (on 183, off MacArthur). It is extremely sketchy and suffers from at least a decade of deferred maintenance; however, I don't know what it is (probably nostalgia), but I absolutely love their pepperoni pizza.
It sucks that most of the chains are in a price war and are dead set on having their pizza at or below $10; the quality suffers. In the past, Pizza Hut and Pizza Inn had decent pizza at reasonable prices; but, they've both gone downhill in quality.
-As far as the cheap, cheap places go, I kind of like the $5.55 Little Caesars pizza that is already cooked when you walk in the door. By no means is it good, but certainly not bad for $6.01 after tax.
-I don't think Papa John's, Domino's, or Pizza Patron (a Dallas hispanic chain) are even edible.
As for my best pizza experience, a random place I went to in Seattle in '05 or '06 stands out in my mind. I think I was turned onto it by a thread similar to this one on one of the old OU message boards (probably OUInsider). Unfortunately, I have no idea what the name of the place is or if it's even still there. They cooked the crust, sauce, meat, and cheese in the oven, then threw fresh herbs and greens on top right before they brought it to your table. It was essentially a hot pizza with a room temperature salad on top of it.