So, first I'll do a little comparison: (which is pretty simple, mundane stuff, really)
Swords strike at the bearer's initiative and strength (duh). A standard SM Sergeant with a power sword is going to get 4 attacks on the charge, and against T4, he's going to kill a single marine in combat (4 swings, 2 hit, 1 wound). If he's charged, mathematically he'll do less than one wound/round. Guard players need mass power weapons or Straken to actually be dependable. More on that in a little bit.
What's that? Everyone knew all this already? Oh noes! Alright, lets get into the meat of the article.
Power weapons/fists need to be taken with the context of the unit they're with. Lots of times, people will give a Sergeant a power weapon because they don't know what to do with those extra 15 points they have, and it seems like a simple enough solution. They don't bother to think that perhaps the points would be better spent, oh you know, on a combi-melta that will actually contribute or something.
Remember, we're looking for something that will add to the army in a positive, efficient way.
So, what do you expect your squad to be able to do? If it's a tactical squad, what are they good for? There are certainly some instances where tactical marines are good in combat, but against a good combat army, they generally don't last for more than a single round of combat. In fact, against good combat armies, a single power weapon won't really put any sort of a dent in the opposition. It'll at best make a break-even contribution. Against armies that suck at combat and you want your marines to charge them, the power sword is oftentimes unneeded.
- Squad itself gets 30 attacks, the priest gets 4
- Squad does 10 wounds (15 hit, 10 wound), priest does 1.7
- So, total of 12 wounds caused
At the same time, this is why I like fists on combat units so much. I actually like that fists strike at I1. It means that whatever damage you caused with the rest of your squad is already in effect, and every single wound caused by the fist will have significance. More bang for the buck, see? :)
Power weapons certainly still have their place in some lists, however. Guard can take an obscene number of pw's in a single big blob squad, and because of the volume of attacks they put out, their attacks still have a huge impact on squads they're in combat with. On Blood Angels, my example was for a 10-man assault squad. 5-man assault squads oftentimes won't do 10 wounds in combat however, taking a sword on the sergeant is oftentimes preferable to a fist (vs. T4 a pw will do 1.7 wounds on the charge vs. the 1.26 a fist does)
In lots of lists, a power weapon/fist doesn't add much at all. A combi-flamer will cause more overall damage than a fist or power weapon many times, and it's cheaper. The key is to know what to expect of your squad, and know their limitations/strengths. Killing an extra marine can be huge, but you have to take it in the context of the overall picture. If half the points you're paying are being wasted, it isn't being put to good use.
There is also the factor of versatility. If you buy a power weapon, you're essentially relegating those points to be specifically for anti-infantry. If you buy a fist, a squad can threaten any number of things, including vehicles, MC's, and characters. Those extra 10 points you pay for the fist ensure that you have more options for your army. Sometimes it's worth it, sometimes not.
There's more to it than just this, of course. A unit with all power weapons is a completely different animal than a unit with just one. Beware using a unit with mixed pw's and mundane attacks. If even one mundane attack gets through, a player can roll the save on his sergeant, (or whoever he wants) and survive to strike back at you. For example, if you cause 18 power wounds to a squad, and a single non-power wound, a full squad of 10 dudes will die, except for the sergeant w/ fist, who will take the save instead.
Lots of other things to consider, but I think I'll leave it at that. For those of you who are still reading, first of all, good job :) Second off, what do you think? It's a somewhat touchy matter, and I'm interested to hear your view on it.