I agree; while the Wavemaster is probably the most well known free standing bag, it has it's major drawbacks.
I find the regular one I have fine for kicking, but it does move a fair amount. I'd also NOT recommend filling it with water----the weakest point is where the base meets the neck. Unfourtunately, this is also the point that takes the greatest amount of stress.
We've gone through about 3 in the past year at my TKD school; the heavy bag, which we've had for many years, is in fine form. In fact, the chain links holding it have had to be replaced, but the bag is fine.
Also, it may just be my wavemaster, but it's hell on the wrists; while I can pound a heavy hanging bag with no problem, the wavemaster made my wrists aches for weeks after a few sessions of un-wrapped punching.
If you have no option for a heavy hanging bag, a wavewaster is better than nothing, IMO.