Ground war is pretty much the best you can get - period !
Airwar is biased towards lowlevel fighting / bombing.
Machine requirements are very high - specially for flying - ground war can
be done with a lesser machine.
Navy is also pretty fun but gaining enough rank to sail our capital ship the destroyer is pretty tough. The naval aspect of BE has progressed over the years from the navy being essentially a blue water fleet to more of a marine unit. As it stands now naval personnel do more amphibious/paratroop operations than sailing.
Naval is limited essentially to three vessels, the farmile, the freighter and the destroyer. The farmile is a disappointment to most players if they take them out on the sea's and encounter enemy air or lord forbid a destroyer. The freighter is a cool piece of equipment that can make an impact on a campaign when loaded with it's compliment of 4 player supplied tanks. The island towns in BE aren't equipped with armor so when a freighter offloads tanks and they show up in an opposing forces island towns you open up a serious bee's nest. The destroyer is a nice piece of equipment and is the top tier vessel for navy guys. It's hard to rank up enough to be able to rate for one but it's darn nice when you have the ability to touch off a salvo of 5" guns. Ground guys hate us when we pull into a port and start leveling the town.
The naval aspect does need some work and has been somewhat neglected the past several years. CRS is working on an actual "mission" for the navy in the way of supply chains that effect each countries overall supplies and RDP but it can't enter soon enough for me. They also have to introduce a surviveable blue water vessel beyond the farmile that young players can easily rank to and introduce a smaller troop carrier or barge that allows for easier amphibious operations.
I'm sorry that I didn't know that this 14 day trial was going on or I would have asked some of the Royal Navy to take guys requesting out on a multi-crewed destroyer for action.
All in all WWIIONLINE provides a person interested in war gaming and strategy the most oportunities I've encountered since 1996 in the gaming world.