Well, here's my 2 cents..........
You can't go wrong with either the Marauder or the Disco. I have both and both are outstanding rifles. The 10 shot rotary clip on the Marauder is simply outstanding while hunting, especially tough critters like squirrel in case you need a fast second shot or if you take down one squirrel and there's more in the tree :) The Marauder also comes already set up for a sling, which is nice to have since the Marauder, while not too heavy, has some weight to it. The Marauder is so quiet it's amazing, another big plus in the hunting situation.
Now for the Disco........ very light and easy to carry all day long. Excellent power and accuracy (just like the Marauder) but yet this power is achieved with a fill pressure of only 2000 psi. This 2000 psi fill gives you a ton of fills from your scuba tank, much more than a rifle needing a 3000 psi fill, and that 2000 psi fill is especially appreciated if you're going to be using a pump to air it up. Drawbacks to the disco.......... the stock can be a little "small" for a full grown adult, although I've gotten used to mine, and in it's stock form it's a bit loud (although that can be correct). Also, keep in mind for around $369 bucks you can get the disco/pump combo which means you are all set to start shooting and or hunting as soon as you open the box. With the Marauder or other PCP's you have to buy the equipment to air it up.
Since both the Mrod and the disco are from Crosman you know you will have outstanding customer service support and an easy and inexpensive supply of spare parts, extra barrels, etc.
For someone diving into PCP's for the first time my 2 cents would be to go with a disco. Personally I think it's the perfect shooting platform for a beginner... or even an "expert".
As for the pneuma.......... I don't own one but I have shot them and I was not all that impressed. The ones I shot were a bit loud and I've heard of some air leakage problems with them. I'm not sure how they're customer service dept operates but I doubt it's as easy as dealing with Crosman.
Ok,,,, there's my 2 cents............. other members may have different opinions I'm sure.... but those are my thoughts :)
Jeff