Hatsan makes some nice guns. The extra pound of the BT65 over the Marauder gets you double the shot count. It also has a field changeable air cylinder (if you buy another). And the cylinder houses the valve, so you can have one tuned for max power (PAL) and another tuned for max shot count (non-PAL) or field target, etc.
That being said, the m-rod is getting a lot of attention from the tuners and customizers right now, and the velocity is adjustable out of the box. Upgrade and spare parts will be easier to get. Also, I'm not sure if the BT65 is current production any more.
I would get the Marauder. I would also get a couple extra mags.