I have an RCBS reloader starter kit (for20yrs, never used) that I am finally going to set up to reload for my new CZ527 .221 FB. What type/brand of dies should I purchase? Thanks.

depends on how much you want to spend. I use either Redding (first choice) or RCBS (second choice)

All of my reloading dies are RCBS! No problem with any of them in over 25 years.

But from what I can make of it, brand is simply a matter of personal choice, I believe they're all good!

I have never had a problem with Redding, Forster, or RCBS sizers, but have had problems with Lee and Hornady. But the seater die for Hornady and Lee are quite good. If RCBS would improve their seater, they could get more of my business.
Overall, I prefer Redding, and I use their 3-die set for my Fireball.

Redding

Ditto on Redding.
JCN

Mine are Redding but I have had excellent luck with almost all of them.
Good choice of first cartridge to load for.........plenty of good combinations and accuracy is superb in most guns.
I like RL-7, Lil gun, AA1680 and H4227 in mine under a 40 v max.