I bought a xb2003 this past summer, so I'm new to the game, but I've done a lot of research over the years of wanting an Allison. Your setup is probably the most common allison out there, so there has been a ton of discussion on props for our rigs. Spend some time using the search function at the top of the forums page. Just type in something like "best prop xb2003" and you'll get all the historical posts on this subject. I would do this on this forum and all the other forums you routinely visit ( i.e. screamandfly, fastbass, etc....) I've learned a lot doing this same thing.
I'll give you my 2 cents worth, but I haven't personally ran many props yet. Here's what I've learned from the years of reading the boards: Our boats seem to like the big ear props like the big ear merc choppers or Mazco RE3 or 4. Being that choppers are readily available used and are relatively priced lower, I think this is a good place to start.
You'll find a ton of people that love the Hoss props, both the Triton 1 and Hyperdrive. There also seems to be a big following for the Hydromotive prop too. Try as many as you can and talk to as many people as you can.
The two props I've ran are the 26 Trophy Plus and a 28 Merc ET. In my opinion, the Trophy is a pretty good prop and its what I learned to drive with. Handles good, and with a stock rev limited 225 promax, my boat runs 88.7 mph. At that speed, the prop is all over the limiter. I didn't have enough seat time to give the ET a fair judgement, but it came out of the hole great and had a lot of lift (I think it was worked for my buddy's 21ft. Bullet). It seemed to have a little more steering torque, but it may be that I'm used to a 4 blade. General consensus is that the 4 blade handles a little better on average, but the 3 blades are generally faster on top. If you have the stock rev limiter I'd say start with a 28. If you're non-rev limited, most people seem to like the 26. I'm in the market for a 28 allison cut chopper as we speak!
You came to the right place! Hope I've helped some.
Mark