For the states listed, I can only speak for Idaho (and Colorado.) You have four things to consider in the rifle purchase:
1) Conical vs. Sabot
2) 209 vs. traditional ignition like #11 or 209
3) Inline or sidehammer
4) Open sights, peep or buckhorn style (that one is obvious, but I thought I better throw it in)
After that, it's just components like loose powder vs. pellets, bullet construction, and powder type (for example, smokeless is illegal, as in Blackhorn 209 in some states like NV.)
For the rifle, consider that are going to be restricted to a conical bullet (non-sabot.) This means you want to buy a gun with a slower twist than a gun made for sabots, if you'd like less than 4" groups.
Most sabot guns shoot best with fast twist, like 1:28 or faster (faster means smaller 2nd number, so 1:12 is faster than 1:28) and since most of the US allows sabots, most guns are fast twist these days.
If you are going to hunt with conicals, it is best to start with a gun with a 1:48 twist as they stabilize conicals better. Trust me on this one, I spent all summer trying to get a T/C Encore with 1:28 to shoot conicals and it won't do it. It shoots sabots very well. Many of the guns listed above will be available in 1:48 twist, but you have to check!
For Colorado, you can use 209's, but Idaho you must use #11 or musket.
Both Idaho and Colorado allow "inline" ignition, as in you don't have to have a sidehammer, but Idaho requires that the cap "must be exposed when cocked to fire", so a sealed ignition system is illegal. Colorado allows a sealed ignition system and is one reason I tried so hard to get the T/C Encore to shoot.
Open sights, with no electronics. I don't know for sure if fiber optics are allowed, but I don't use them anyway.
From there, it just gets into bullet construction type and the rifles that shoot conicals can usually do fine with any bullet construction. Idaho only allows bullets made fully of lead, so a copper jacketed bullet, even if it is conical, is illegal. Not so in Colorado.
Keep us posted on your purchase. I have a thread on the muzz forum with video called "Big Mule Deer Here I Come"
http://www.rokslide.com/forums/showthread.php?1148-Big-mule-deer-here-I-come-)
if you want to watch my painful process of getting a muzzleloader to shoot well. By the grace of God, I finally got it, but it was not easy. As usual, though, I learned a lot.