Honestly, what it comes down to IMO is platter size.
If you’re okay with a smaller platter, either the CDJ-400 or CDJ-350 will be perfect for you. I’d suggest testing both (I like the 400’s platter much better personally) and deciding about that.
Otherwise, the 850 is the wave of the future. It’s got the larger platter, and all the necessary bells and whistles of the newest generation of players. It can do everything the 400 can do (besides on-board effects, which IMO should be on the mixer or an external controller anyhow) and also has use with rekordbox and couple other newer features I can’t think of off the top of my head.
Honestly, also think of size. The 400’s are much smaller than the larger variety of players, and so if you plan on moving your setup at all, it’s a lot less you have to move around. (Thinking mainly for house parties and the like). But if you plan on basically having a bedroom setup, and keeping it in one place, then it won’t matter what size it is.
I’m debating the same thing at the moment really. My $$ got pushed back a bit because of Christmas and also planning a trip to Ultra and Key West (Thur-Sun Miami, then Mon-Wed Key West).
If you can get a deal on used 400’s, or even refurb ones, it’s an excellent use of your cash. If you’re forced to buy new, then I really think it’s worth the bit extra at that point to just go out and get the 850’s, unless you want as small a setup as you can get.
Vanity wise, the 850’s also fit the size of most mixers better, and so I think they look more solid. I really do like the look of the 400’s however, especially the unavailable limited ones, and it just comes down to what you prefer.
Any choice listed above will do you right in the end. But I think the best long term “buy once and not regret it” would be the 850’s. Unless you score a killer deal on 400’s.
