Milviz did a much better job simulating weapon, and the associated systems with it. Right now you can enjoy blowing stuff up on the ground, and shooting aircraft out of the sky in both single payer, and mulitiplayer. Milviz spent a lot of time tweaking the flight model to get the "feel" right with help from a real world F-15 E pilot, when the mudhen is loaded down with a bunch of weapons, she is a heavy bird, and she flies like it too.
For the weapons, in Air to Ground mode, both guided and unguided weapons work, the laser designator is simulated to help guide the maverick, and LGB's , with nice explosions to see your handiwork being done.
Air to Air mode all radar modes, and air to air weapons work, including the guns. Also there is a chaff a flare system, which works in both single and multiplayer modes, but in MP mode, the flare system works to help defend you against another players missile, it's not just there for eye candy.
And you get a free scenery and AI F-15 pack, that has F-15's from their real world operating bases, along with the AI pack, you get a mission pack to enjoy your F-15 with, AI and mission pack are free.
Don't want to start a war, and searching the forum there is a ton of information here, as well as both companies forums. I guess it comes down to what you like in your sim. I do a lot of mulitplayer flying, and the weapons and systems modeled in the milviz bird is what I prefer.
If you can afford it, get both, both companies would appreciate the support.
Jon