This is not a simple question or answer. In general, the lighter the better from a performance standpoint. 12" wheel/tire combos seem to be lighter overall than a like diameter setup with a larger wheel.
Maxxis 4 Speeds are the lightest tire you'll find and work great for MX and short course if the track is groomed well or dry and hard. If the track is muddy, you'll be all over the place. On top of that, an XP's power is probably pushing the traction limit of a 4 speed tire. The 4 Speed is also a little short on height for an XP.
A combo that I really like on the XP is the Maxxis Ceros tires. I also happen to have them on my XP and I have run them on a built Teryx. Depending on how competitive you want to be, you might need to groove or sipe the tire.
The Bajacross is a durable tire but a poor choice in my opinion. Waaaayyy too heavy for MX application. One of the heaviest tires you'll find.
The General will be a much harder compound, and will be heavy. I think you'll be disappointed with traction and the performance due to rotating mass.
For wheels, all the companies you mentioned are good. Each have pluses and minuses in my opinion. I like the DWT Sectors but they don't offer them in a 14" or 15" diameter. Spun wheels will be the lightest but you chance bending them if you are jumping very hard.
Hope this info helped a little!