Good points, Etym.

Another consideration (for me) is whether I prefer to use my troops elsewhere in the short term. Even if battling rebels are generally easier than faction troops (they tend to rout faster), my armies will usually take losses, and if they are better spent on a more worthy opponent, then bribing may be a quicker solution.

You may also have fewer province loyalty problems, since you will have more men occupying the province than you would after a bloddy battle. But the first consideration is definitely the money :-)