The Warlord one is on the left and the BTD on the right. The most immediate difference between the two is the tripod mount. The BTD one is thick and heavy. This gives it some welcome sturdiness. It also makes it way over-scaled. The other problem is that the stand looks very two dimensional.
The Warlord stand is far more accurate in scale. It also spreads out in three dimensions. But it wasn't easy to get there. The legs come flat and there were no instructions. Fortunately, I found a picture of the entire stand. So it was a matter of delicately twisting and bending the legs until they were the right shape and fit with the gunner. Of course, this meant that a stand was an absolute necessity.
The figures themselves are similar in size and chunkiness. The Warlords are a little more impressionistic while the BTD are firmer in detail. The difference shows up more when you are actually painting them. You have to use your imagination more for the Warlord ones while the highly raise details on the BTD make them easier pop them.
Overall, I generally prefer BTD figures but the Warlord ones blend in pretty easily and nicely supplement the gaps I had in my troops.