I always like to recommend getting a BT SA-17 with Rifle Kit. It's a pistol type of marker that can be converted to a more regular style marker with the Rifle Kit.
The reason I like it is because it's very reliable, easy to take apart and maintain, it's simple operation and the way it uses barrel inserts to let you choose the bore of your barrel. The reason it makes a nice beginner's marker is because at a later time when you want to upgrade to a different marker, you can always remove the rifle kit and you have a very fun pistol to play paintball in a completely different style. The barrel threading is autococker threads which means that any barrel that you buy for the SA-17 will fit onto the majority of other markers you may possibly own in the future.
So yeah, to put it simply: You get the SA-17, attach the rifle kit. Use that for a long time. (really simple but one of the nicest "simple" markers out there) ,when you upgrade in the future you detach the rifle kit, when you feel like it you can use it as a pistol type marker and have a lot of fun running around a heck of a lot and stuff and adopt a completely different playstyle for the SA-17 while keeping your regular playstyle for your new marker