I have a highball trackball, and I'll never get any other kind. I feel like I have twice the control of a normal trackball with it because I can keep more of my hand in contact with it. Kind of hard to explain, but believe me it's worth it. If you ever happen to see one of those multi-Centipede/Millipede cabinets, I believe it has a high ball trackball in it.
I prefer normal (& high lip) TBs very much over the high ball TB. It has to do with how I use TBs. The high ball sticks so far up that the sides to so vertical, it hurts my hands when I hit it from the side, which I do quite a bit. Sounds like ahofle "stays on top of" the TB, so doesn't have this problem with it. Also, on the high ball TB, the ball comes off the rollers a lot more often than normal (& high lip) TBs do, causing skips. Again, this probably has to do with how I use the TB more "from the sides" than on top.
Another difference: the high ball has a slightly larger mounting plate (the case is the same size). This forces close buttons farther away (unless you drill the plate, or mount it without the plate). And makes a surprising difference on fitting it on CPs.
OTOH, if I had a lexan/plexi cover on my CPs and mounted the TB under the cover, a high ball TB might be low enough for me be able to use it.
Like joysticks, whether the high ball is better for a person depends on how that person uses the TB, how he's mounting it, and the CP (size, spacing, thickness, etc) it's being put on.
... Is this also so with the high track ball? The regular trackball? And what do any of you think of the 2 1/4" trackball?
No, no, and too small except for cocktail CPs.
Would it be better to buy the USB trackball instead of the normal Trackball and an opti-pac?
I'd say it's cheaper to go the USB trackball, except
if the USB sensor board goes down, you have to buy a new one (it happened to a post recently), plus looks like happs puts the USB version at a $60 hike, which isn't cheap. If you went with a normal TB and optipac (or minipac, mousehack, etc), it would be easier with more options and probably cheaper to fix if one part stopped working.
And why is the trackball mount so much pricier for the non usb mount?

Shouldn't be any difference, unless you're talking about the newer "heavy duty" (aka "golden tee") mount vs the older mounts. The newest mount is cheaper, probably due to volume of sales, even though it's supposed to be a better mount (I don't have one).
Also what about the high ball trackball assembly? What benefit is there to buying that one? I assume its so the ball sticks out more on the panel but do I really need that? my CP will be made out of 3/4" plywood plus perhaps 1/4" plexi. Will I need the high ball trackball? And do they sell the high ball in USB?
Already mentioned a little above (I don't like the high ball), but with a 1/4" plexi + art over the mounting plate, I
might lean toward the high ball. The high ball lip is 1/8" tall, the mounting plate 1/16"; that would put the top of the lip 3/16" below the top of the plexi, even before the thickness of the art is counted in. If the plexi was 1/8", I'd get a high lip: sink the 1/16" mounting plate into the CP, the high lip's 3/16" lip would be flush with the top of the plexi.