Plenty of discussions in this area on other active threads. But, if it were me, and I only had 250k in each account, I'd still go with CD's. You didn't say how long you wanted to go out with the ladders. 1yr, 2 yr, 5 yr. Regardless, if you think the Fed is going to raise rates 1 or 2 more times this year, (I do too) you might want to buy some very short term CD's now (3 to 6 mo) and then re-buy longer term CD's when they mature and after the Fed raises rates again.
OR, just park your money in a Schwab's Money Fund like SWVXX until you think the Fed is done raising rates and then buy/build your longer term CD ladders with those funds.
I like CD's that pay monthly so I can reinvest the interest along the way. Other than that, just be sure the brokered CD's you are buying are non-callable and FDIC insured. Most are and very easy to see/do at Schwab.
Nice thing about doing this in an IRA is you don't need to worry about any taxes.... YET!