A random, incomplete run down of my take on dies:
RCBS is my standard.
Hornady, in my opinion, is about the same as RCBS, but their dies are machined fairly roughly at times.
Redding is a nice upgrade.
I love my Forsters, but they're pricey.
Most of my recent purchases have been Hornady, because, well, "free" bullets at the same price as the competition, or they offered something that no one else did (or had the best price on custom dies).
I won't touch standard Lee dies unless I have no other choice.
I don't buy Lyman dies, except for the M dies/expanders. They're good dies, but Lyman's customer service has gone to crap and the dies are just overpriced.
Lyman M dies are a very nice tool to have, but not really necessary unless you get into cast bullets or bullets that tend to hang up on case mouths.
I do not have a problem buying used dies. As long as the price matches condition and I can inspect the item(s), I'm good with it. If I can see minor scratches in the sizing, for example, but the 2-die set is only $8, I'll probably take a chance on it. If the die is so dirty that I can't even tell what it is...? No, not going there.
Shell holders:
Try to figure it out early, and stick with the same brand - or at least compatible tools.
I have grown to hate Lee shell holders. Too sloppy. Too tight. Too variable. Too incompatible with some other brands of tools. Lee's approach of "one shell holder fits 27 cartridges" is, in the real world, more like, "one shell holder sort of works, some of the time, for some of the cartridges, and may not work at all for the rest of them."
RCBS, Redding, and Lyman are about the same, and decent.
Forster are good.
I have come to prefer Hornady shell holders for consistency and proper dimensions.
But, of course, you may need to consider your priming tool and/or other accessories like a case trimmer, when looking at shell holders. My Hornady trimmer, for example, ONLY works with Hornady shell holders. No other brand works with that tool. Any cartridge that I intend to trim cases for requires a Hornady shell holder.
But, of course, yet again... My CH-4D primer pocket swager needs a little more support for the case rim than the Hornady shell holders provide (due to the taper machined for easy insertion). So, I also need a Redding or RCBS shell holder for cartridges that get the primer pocket swaged.
But, wait, there's more! My RCBS priming tool, at least in factory form, doesn't get along with Hornady or Redding shell holders, and really hates Lee shell holders. So, RCBS shell holders are required, unless I modify the tool (which is what I did ... just enough for Hornady shell holders to work).
So, I have primarily Hornady, RCBS, and Lee (learned the hard way) shell holders, but also have one to five each from: Pacific, Bair, Forster, Lyman, Redding, CH-4D, and a couple others.