I voted for Forster as it's my preferred brand, but in fact I own all of those except for Hornady.
I have several comments on each and maybe there's value in this for others...
Lee:
Now my preferred brand for handguns (revolvers and semi's, not speciality type stuff). I've used all brands for these and Lee works just fine and I could never see any benefit in other brands.
I use the collet neck sizer for several rifle calibers and I am very happy with them - but they need some tuning and smoothing in my opinion and I object to that. I've also had one with the bottom of the sliding sleeve cut at an angle.
I've used the regular rifle dies too and I like the idea of the long expander "ball" for full support. A nice idea and it works.
The seating dies have been singularly disappointing. In 375 I could not adjust the dead length seater correctly to seat the bullets. In fact another set of Lee 375 dies were similar but not quite as bad. The seater plug needed to be backed right out together with the die to accommodate the COAL.
Lots of good ideas, some poorly executed.
Redding:
I've used the competition sets with good results (I also have a set for some of my revolvers). I don't really have any negative comments about these. I don't really like the lock rings and if you are one to tighten them they don't loosen up easily again with that piece of lead shot. Not a big deal though.
I haven't really had my best results in straightness with body dies that the Redding comp set includes. I've used them together with Lee Collett dies in several calibers and actually found that runout increased markedly when bumping the shoulder. I think that the unsupported neck in the body dies are the reason for this. I now prefer a full length sizer when I intend bumping the shoulder.
I feel the price is high for what you get, particularly on the seater die.
Obviously comments about bushing dies relate to the concept and I haven't found fault with Redding's execution of the concept.
Redding's regular dies are a slightly different beast. The expander ball is low in the die and I believe this contributes to higher neck runout. I adjust my "regular dies" like Kirby (I think it was him!) recommends, which involves screwing the expander up so that you create a situation where there is a degree of support from the neck area of the die. With a regular Redding you can't do that.
My experience is that the Redding dies I have seem to size the case body more than some other brands ( i.e. they are towards the tighter end of spec).
RCBS:
I've got a bunch of older RCBS dies. Both in handgun and rifle.
No complaints and as far as regular dies go, probably as good as any. I can back out the expander ball as described earlier and I've loaded some really straight ammo that way.
The seaters are the same as other regular seaters, and work fine. Mine are admittedly older dies, but they seem to size the bases of my cases a bit less than Redding and Forster (certainly in the calibers that I've used them in).
Forster:
right now these are my preferred choice. The reason for this is based on the expander design and the seater. The expander provides a supported type set up much like I described earlier, but it's designed like that and doesn't require backing out the expander to accomplish this. If you aren't up for decapping separately (which I recommend anyway), this is an advantage. In my comparisons sized cases are no straighter than an RCBS die adjusted as per my suggestion. The sizer seems to size the body of the case a little smaller than other brands as does Redding.
If I were in the US, I'd seriously consider the factory honed necks on the sizer dies. I'm trying to see who here would be up to the task.
The seater is great and whilst the finish might be little more homely than Redding, it's just as good in execution and as far as I know Forster pioneered the concept and the other guys copied it. There's a benefit in having the offering without the micrometer top and Forster gets my nod for a great product at a great price.
That's pretty much my input. Redding tech support is unbeatable. The website has some great "tech tips" and queries are quickly and coherently addressed. My queries addressed to Forster always seemed to recive a response that didn't answer the question (and I don't think my communications skills are that poor, although my girlfriend may disagree). But that's not input about the dies...
For my money I recommend Forster FL Bench Rest set without the micrometer top (although the extra cash is worth it if you change things often) and a Lee Collet die. I deally I'd have the neck of the sizer honed to suit my components. Alternatively I've had good results with the sizer and an expander mandrel, but the question was about dies!