Yeah EE seem to be the best network these daysCertainly better coverage than they used to be, to be honest I have the best of both worlds now as the mifi is with me, so if it's looking like a ropey o2 signal I can use the EE mifi. EEs speeds are without a shadow of a doubt much faster.
Here at home, upstairs I can get home broadband type speeds, 40-60mb down IIRC for example. We appear to be in a location with their fastest 4G, I could probably get more if I went outside...