I know that it's past the point of getting either of those rifles, but here's a couple of points to help you get your eye in for a nice flintlock.
That top one, the Traditions, is way too short. Looks like a kid's gun with maybe a bit of a long trigger pull, or a normal gun with an unreasonably short barrel. I'm not saying it won't shoot well, but for a traditional muzzleloader kind of guy, it doesn't look right. Proportions are all wrong.
You may not care about all that now, but if you do this enough, you will in the future.
I've never had a Lyman Great Plains rifle, but they are generally well known to be good rifles.
You said you are new to muzzleloaders, good on you for wanting a flintlock!
If you have the means, I would advise you to get a decent one. Flintlocks can be difficult for newbie's, and if you buy a cheap one, it will be even harder. You gotta have a good lock, or you will likely just get frustrated.
Pedersoli makes some good flintlocks, with good locks. They are more spendy than others, but worth it.
I don't own, or have never shot a traditions flintlock, but through hearsay I would say that their locks are not all that good. I'm sure someone will pipe in with both positive/negative on them.
Also, you asked about shooting bullets ( I assume you mean conical bullets rather than round ball). Personally, a conical bullet in a flintlock is like surround sound with bass woofers pounding out R&B in a Model-T car. Just not quite right. Also, if you get a .50 or .54 you can hunt just about anything in North America with a round ball.
For round ball, slower twist is your friend. 1 in 66 or 1 in 48 or something along those lines. You don't need fast twist to stabilize a sphere.
Do a bit of research first, and I think you will be glad of it. There are folks here who are smart about it, and there are plenty of other muzzleloading forums as well, tailored to the traditional side.
Cheers,
Chowmi
