Sue:
If you want to maximize size you'll do fine with the german extra hardy that you got. Northern White is a very similar porcelain type and probably not worth the effort, because it is so similar. The clove shape of NW is slighly more rounded at the tip. That said, GW or NW or Music from different vendors might not be indentical due to the presence of virus.
Soil fertility, water, and spacing, and climate factors like severity and length of winter, and sunlight, play a big role in size. so does growing virus free stock.
There are other garlics that are interesting for flavors and colors but the porcelains grow the largest bulbs and tend also to have the largest cloves. Storage might also be another consideration. I always have a few purple stripe and marbled purple stripe varieties in the mix. If you're serious about garlic I don't think you'd regret a trip to Saugerties
http://hvgf.org/