I do almost all my splitting with a 6 lb splitting maul. I've never tried a Fiskars axe or a monster maul, simply because, I've never had any problems with the 6 lber. I hear great things about both though.
I haven't met much I can't split with a 6 lb maul and a good set of wedges. I always keep three wedges on hand, one with a narrow taper that's easy to start. I did add an 8 lb maul to the line up and occasionally reach for it if there's something I think I can get without wedges but won't go with the 6 lb.
If you just want a simple, traditional maul to start with, just make sure you buy a quality one with a tempered head. Fiberglass/hickory/ash handle is mostly preference, but it pays to get a quality head, especially if you use the hammer side for driving wedges like I do.
I have a friend that bought a Chinese made Home Despot special and after a year of pounding wedges, the hammer side was cracked and mushroomed.