I really enjoy replica airguns, usually more than the real thing, so I've got quite a few.
I've got Glock Gen4 and Gen5. The Gen4 is much more realistic in terms of trigger pull and function. It even field strips much like the real thing. The Gen5 fires pellets and is more accurate and more powerful, but has an atrocious trigger that really can't be made any better than bad. It's also not as realistic in terms of function.
I've got a Barra Schofield in .22 and it's pretty good, but I think the Dan Wesson replicas are better.
The Barra 400e is perhaps the best BB gun made. I've shot all of the BB guns I consider accurate off a bench and it's the most accurate of any I have shot. It's not the most realistic replica, but it's the best BB gun overall IMO. Very expensive though.
The new Crosman M1 Carbine is also an excellent BB gun considering the price, which is very reasonable. It's also very accurate for a BB gun with very good sights and it has full auto and is very efficient with the CO2. It's not particularly realistic, but considering everything else I'd highly recommend it. Dollar for dollar I'd rate it above the Barra.
The Umarex MP40 is excellent and a lot of fun to shoot. It's both very realistic and very accurate for a BB gun. This is my #3 pick overall.
The Umarex M1 Carbine is extremely realistic and more accurate than the Crosman, but it's a CO2 hog and uses expensive 15 round magazines. If you're into Larping or something then get the Umarex. If you just like plinking and having fun, get the Crosman.
The Crosman MPW is very realistic, but accuracy is marginal and magazines are pricey. Kids will think it's awesome though.
My Springfield Armory M1A has been a turd and I really wanted to love this gun. It's a full size wood and metal rifle that looks and feels very close to the real thing and is quite powerful for a replica, rated at 800 fps in .22. It has good iron sights and is quite affordable. Mine has been a super twangy, minute of can rifle at 20 yards however and I've yet to find a way to make it shoot accurately.