What's the best kit gun

[bob in the woods]

Memory just kicked back in      Check out Tip Curtis.   He had just about every style of long rifle and smoothbore you could think of the last time I talked to him.  I hope he's still in business.  He also had a tremendous stock of barrels at the time.  Definitely worth a look.

[Acer Saccharum]

Consider skill level when picking a kit. If you're thoroughly versed in gun building, any of the kits will be fine. If you've never done this before, the Kibler is the easiest to put together. Most other kits need careful fitting of metal to wood, with varying degree of difficulty.

[taco650]

Have you looked at Tennessee Valley Muzzleloading's kits?  They are pretty affordable and come in two difficulty levels ("Builder" or Standard") or completely assembled but "in the white". 

[smokepole45cal]

A lot of seasoned builders will tell you it's actually more difficult to build from a kit than starting from a blank. Not disrespecting kits...to each his own preference. But I've seen an expensive Chambers kit ruined as a 1st time build because the builder thought that was the only way to learn. Maybe consider piecing together your own projects at a better price and following a more unique profile/pattern that is adjusted to your trigger pull length from "RCA I and II" or "Thoughts on the KY Rifle in its Golden Age"?