The standard answer:
Ignoring the search function, the use of which would turn up numerous threads on this topic...The Armi Sport US Model 1842. Best reproduction musket "out of the box" to date. There is a 150th anniversary edition, which is not worth the extra money but is nicer. Also a very cool rifled version with a long range rear sight. It works for US, CS early to mid-war especially but it is not out of place at virtually any event. Plus smoothbore muskets are under-represented in the ranks.
If you want an Enfield, the Pedersoli P53 requires much less defarbing than the Armi Sport version. Like the 1842, it is pretty darn good right out of the box for about the same price.
Craig L Barry
Editor, The Watchdog in Civil War News