There are a huge number of mixed letter and number (cccc.coms) still available. Unless there is a clear, salable meaning those are not recommended.
All four letter .coms will be sold out within the next year (maybe sooner) unless the trend changes. But the better ones will be worth more than the junk. Problem is, while the best ones are rather easy to determine, what looks like junk may not be junk. Zmnm.com just pulled 10 grand, making many lesser quality LLLL.com owners' hearts go pitter patter.