In-lines I have experience with are the MDM Buckwacka, Encore, and the Savage ML ll.
The Buckwacka is a nice short barreled bambi blaster. It will handle 150g loads with no problem, but it does kick like a mule. It will shoot minute of whitetail out to 100 yards. Its small and reliable. Best I have gotten was 1 1/2 inch groups at 100 yards. I have no regrets with this one.
The Encore is a little finicky. Shoots great, and I like the ability to change barrels to a center fire. It is over-priced in my opinion. Best I have gotten was 1 1/4 groups at 100 yards. The barrels are very tight, and if you go for a center-fire ML, use the MMP HPH24 sabot. Its .02 inch undersized to make loading a tad easier. They are over priced, but they do offer a lifetime warranty.
The Savage ML ll is by far my favorite. It shoots 7/8 inch at 100 yards with SMOKELESS powder. Nice flat trajectory, easy clean-up, and no blow-back. It can shoot any of the BP subs, and smokeless as well. Im shooting at 2300+/- fps, which is a mid-level load that is easy on the shoulder and very effective on game. It can reach out to 200 yards IF the shooter is capable. Totally no regrets here.
All that said, I am in the process of sighting in a 38 inch Lancaster style flintlock in .54 caliber for this season.
Good luck with your decision,
kb