urup,
There are lots of folks on here with more knowledge and experience than I have, so take that into account when reading the following advice. I'm still very much learning as I go..
Hybrids are usually recommended to be stocked alone, or at least with no other Bluegill species. The reason being involves one of the hybrids most attractive traits. (For me at least). That being they are around 90% male, which means they are far less prone to overwhelm and overpopulate their food supply, and your pond. When they are stocked with regular strain Bluegill, they will readily spawn with them and you lose one of the best reasons for stocking them in the first place. In addition, the offspring of hybrids, or hybrid/native combinations, may not possess the other attractive qualities of this fish. Those being such things as aggressiveness, relatively easy to catch, readily accepts artificial food, rapid growth, superb fighters, and the biggest, most often discussed trait... ultimate size potential. Each succeeding generation will typically possess fewer of the qualities you desire, and more of the ones you don't.
As far as to which fish will grow larger, HBG vs. BG? The general concensus among people far more qualified than me says that BG have the upper hand, and I would not dispute this. I do tend to believe that the circumstances and conditions in which the fish are raised will play a huge part in their eventual size, and to the numbers of fish which will regularly and consistently achieve large, or even trophy status.
If your goals include a balanced pond, one in which multiple species of fish are managed in such a way that they compliment one another, then regular BG would probably be a better choice, in my opinion. In a nutshell, that can be reduced to one word... Bass. Do you want a healthy Bass fishery in addition to Bluegill? Hybrids will never reproduce enough to keep them fed, and you will find yourself stocking supplemental forage to sustain them. It all boils down to how hard you want to work at your pond, and possibly more important, WHERE you want your efforts to be concentrated at. There are professionals on this forum who have stocked the fish together, made it work, and produced fantastic results.
What are your goals, and how much effort do you want your water to be?
