It really depends on what version you are depicting. Each company’s kits build up into different versions used at different times for different purposes. You first have to decide which time/version you want to build.
Academy’s M1025 Armament Carrier, M966 TOW, M977 Ambulance, M988 Cargo Truck, and M988 IED Guntruck were the best on the market and are still very good. They have some areas that are better detailed than Tamiya’s M1025/M1046 kits like the undersides and frame. They still hold up well and I still prefer them over Tamiya’s for a basic HMMWV. Academy’s M1151 is very nice for a more modern armored version.
Tamiya’s M1025 Armament Carrier and M1046 TOW are a little more updated than Academy’s with more internal storage pieces and newer features such as mirrors mounted on the A pillar, newer tires, etc. Tamiya’s old HMMWM with Bushmaster kit was a test vehicle with an M242 25mm “Bushmaster” cannon mounter on top. It, oddly enough, used the Italeri model (tires and all) as a base and added the parts for the hard top and gun.
Revell’s M998 Cargo/Troop Carrier and M1038 Cargo Truck are very nice as well for early HMMWVs. The soft top parts are more accurate than the Academy one in shape and size. The base HMMWV is the original Italeri version. The biggest issue with it (and all Italeri versions) are the hideous tires. They don’t represent any actual HMMWV pattern at all. With AM resin wheels, they can look very nice.
Italeri’s versions (M998 TOW, M998 Command Vehicle, M1036 TOW, Avenger, M998A1 Guntruck, M1097A2 Cargo Carrier) are pretty good. The above mentioned 4-seat, soft top command version is probably the most accurate of the bunch. Their Avenger model is pretty nice too. As stated above though, you need to replace the tires on all of them. They can come out nice with some work. Some of theirs were fictional or only test vehicles that were never fielded. These include the Desert Patrol version and SF Stinger pedestal launcher version.
Bronco’s M1114 is a very nice version of an older, 1st gen armored HMMWV. It comes in 3 versions to show how the armor and armaments progressed. It builds up well and has lots of details included.
Esci/Ertl HMMWVs were the worst of the lot. They were really bad, and you should stay away from them. The shape of the hood was way off, and the details are pretty soft.