I don't have an RCBS progressive press. I do have a Rock Chucker RCBS single stage press and all the related RCBS equipment. I also have a Dillon 550. The Dillon equipment appears to be of higher quality. My friend with the RCBS progressive shotshell loader gets good results with his. You really can't buy junk from either of these manufacturers.
For progressives, I lean toward Dillon. I couldn't be much happier with my Dillon. I'd buy another one and this is the one I recommend. Mine is well used, it has worn out some easily replaceable parts that are available in an inexpensive spare parts kit. I've had some adjustment problems with the priming apparatus, but that was readily corrected. I've also had powder fail to charge and that was because I had not properly vertically aligned the rod that actuates the powder measure. In other words, there's a learning curve, but it's worth it considering what you get. After I made my few mistakes, everything has been just fine.
I also got the maintenance kit (grease, cleaners, etc.), and some canned air for blowing residue off the press to clean it. I also have five primer tubes that I pre-fill prior to my reloading session. It takes about 10 minutes to pre-fill 500 primers.
Both RCBS and Dillon stand behind their products. Dillon probably dominates the market for progressive loaders.