There's a wonderful network for both guns. The Marauder in the .25 has a Green Mountain barrel for starters. Now your comparing a bullpup to a long rifle. Hatsan has a AT44 in the long rifle, which use's the same breach and barrel as the Bullboss. But if your comparing dollar for dollar. Your going to get more from the Hatsan. Neither gun's are regulated. The .25 will have a very large bell curve. As a new shooter to PCP airguns it maybe hard for you injoy a new gun with a large bell curve. If I could recommend looking at the .22's, you'll get more shoots per fill. This leaving more shoots on the top of the curve. I promise the 18gr pellet will smash thru any thing you need it to.
Both Guns will shoot put to 75 yards out of the box. With a good barrel cleaning and JSB's pellets you'll hold 1 inch groups. Both guns will start to open up the groups out to 100yards. Id expect 2" group at 100yards with both guns from the box.
Both guns have a wonderful mod network around them. With stocks, regulators, barrels, aluminum airtanks, bottle kits,valves, etc. There also some great tunner's out there for both and some great DIY mod's, like the Bob's mod for the Hatsan.
But I fill the real question your asking is: A bullpup or traditional stock gun.
Now I like the bullpup, but I didn't at first. I had to shot a few thousand rounds thru a bullpup before would ever say "I'm a bullpup lover".
If Ive read into your question all wrong, I'm sorry. If your asking me which of the two Id recommend? I going to tell you to get the Hatsan. The Marauder has a great network around it and is a great gun. But I fill its a jump up in price and airgun knowledge, when you factor all the mods and there cost. It will really become a expensive gun for a first gun. But a really good shooter. I fill getting the Hatsan may provide the gun you need for the budget. When you find yourself wanting a bettter gun. Buy a better gun then. Your experience will be much more injoyable. When the day come's you want to DIY a hot rod airgun, build a Marauder.
Good luck Mont