Hey
@hostkobo .. your original question wasn't completely clear.
Are you simply looking for a good registrar where you keep your domain names?
(based on your last post that's what it looks like)
If so then if you can put up with all the bugs, GoDaddy probably has the best prices for a 1000+ portfolio if you pay about $75 a year for their discount domain club (with a coupon .. message me if you need a coupon code).
Remember that your names to have to be bought/renewed at a specific registrar if you also want to sell your names there. If your names are bought/renewed at GoDaddy, you can still list them at Sedo or Uniregistry or Flippa or almost any other marketplace.
Note however .. the ONLY way a domainer can "thrive" is if they have good names and bought them at good prices. Sub-par domains won't sell at any marketplace.
If you're looking to place your domains at auction .. then the best auction platform really depends on your specific names. Commissions can also very widely depending on your selling price .. so you also need to take that into consideration as well.