First off, the thread, "Winter Coyotes and Bobcats should be merged with this one, well at least Asa's response. I say this only for ease of referencing material on drags.
With discussions on drags there always comes a variety of responses, most, if not all, are valid. Asa (both threads) and Lee have hit many of the main issues. Lets look at points, weight, drag modifications, chain and the effect on the "catch".
In soft ground most anything will leave a good mark. In hard ground (frozen or otherwise) sharp points make a big difference and become valuable. Also in hard ground the weight of the drag helps greatly in producing marks. Hang time, the frequency and duration of hang-ups is more effectively increased by increasing chain length. My experience says this is true regardless of cover or ground. The type of chain is important in keeping the drag on the ground and in bedding but these are more a matter of "chocolate and vanilla than the other features.
Steel drags can be modified, kickers and plows added. Depending on the style of drag, you like, the addition of these modifications can be of significant value in many situations. In both cases the additions will give the drag an additional point of marking, for hang up and the two opposing points will work against each other and in this way tend to produce a better mark.
I prefer bent grapples of 1/2" round stock and forged points with Wimberley plows. "T" drags with fixed or hinged points work just fine. For the most part, it is a matter of either, taste or skill / equipment / raw materials that will determine what style of steel drag you end up using. In any case, for coyotes a drag weighing over a pound with sufficient chain, predicted largely by the terrain and cover, should perform well. I use 10 too 15 feet of machine chain on the vast majority of my drags...I trap open country!
