I have found that in general, the mozzarella brands that are available to professional pizzeria operators are superior to what you can find in your local grocery store. Even up here in Boston where there is a pizzeria on every block I have had to spend hours calling cheese company's and distributors just to find certain brands, or even lines within a brand that I wanted to taste test. Like I have mentioned on the forum before, brands like Saputo make many different sub brands or lines, some with milk sourced form Vermont, and some with milk sourced from Wisconsin. Another broad generalization I can make is that usually the Wisconsin cheeses do tend to taste more creamy, and I have been told by professionals that there is a difference in the cows there and what they eat.
If you can justify buying a 5 or 6 pound block of mozzarella, I suggest going through your yellow pages and calling your foodservice providers to buy in bulk from them. You will save BIG money this way too. Just about everything other than Grande can be had for somewhere around $2.50 a pound, so you are really only paying for three pounds when you buy a loaf of cheese, and this stuff lasts for a long time in the refrigerator. Any time I pick up a loaf or two of cheese I always try to buy a bunch of other stuff they sell so that I am not wasting their time on a $15 order. These places are usually happy to sell you cases of water, soft drinks, and I always get my tomatoes and flour there as well.
Another generalization here, but I have found mild (sometimes called slicing) provolone to have more of that stringy quality than mozzarella. You might be surprised to find out how many of your favorite pizzerias are blending mild (not aged) provolone in with the mozzarella, and you didn't even notice. I have found provolones that taste similar to mozzarellas, and vise versa, as these cheeses are made with a similar process.
Dragone (Saputo from Vermont milk), Poly-o, Sorrento, and Great Lakes are all great tasting mozzarella cheeses that I have found in my local super market. Dragone and Great lakes are less stringy than the Poly-0 and the Sorrento. As you probably know, Grande is the favorite mozzarella of the forum and is pretty stringy. There is no question in my mind that Grande has the best melting and reheating characteristics of all the processed mozzarella that I have tried. If you have not tried it you should probably start there, but expect to pay big money for it.