Need help deciding on the one gun only best choice around $500

In that price range, the options for bullpups is obviously limited. Have you looked at the Hatsan USA website? I believe the Hatsan Bullboss wood 

que, is $550 brand new(.25), and if you look at the refurbished part of the site, you may have a couple of choices like the .30 cal that is very accurate 

out to 100 yds. It's also $550 new but not a bullpup. The Sumatra is the most versatile overall and worth getting as its like having a few rifles with the

power dial and wide range of power. On low, its like shooting a German Springer, and on high power you can shoot a 57 grain hollow point, with

103 fpe, like a .30 cal. All the best.
 
Hatsan USA is running a special until 3/3 on the Gladius and Gladius long in .177,.22, and .25. I have a BullBoss in .25 and love it. I just got into the pcp air rifle world about 6 months ago. I also own a hatsan at44 in .177, they both are excellent shooters. I hunt squirrel, rabbits and other small game. I previously own 4 break barrel air rifles and there is no comparison in accuracy and power. I got the .25 for larger game and knockdown power along with better wind stability.
 
Benjamin Maurader is my choice. I bought a .25 and I love it however I decided to go cheaper in a .177 and bought a Umarex. The gun is fine if you have time to sight it in every time you shoot it. It will shoot very accurately. The problem is the point of impact changes if the barrel touches anything. I bought the after market barrel band and installed it and still have the same problem. Wish I had simply spent the $150 extra and bought the Maurader in .177. Check out Sportsman Guide as they have really good prices on the Maurader.Â