> I want to get some sort of Unix running on my 25MHZ 040 Centris 650.
> 
> There seem to be be two options, both of which are to be released "soon."
> 
> 1) MacLinux
> 2) MacBSD
[...]
> First, which is "better"?

 MacBSD most likely won't run on that machine. No information about
linux.
 Linux is supposedly somewhat faster and more SysV-ish and written
pretty much from scratch, while NetBSD is stabler, and is based
on the 4.3BSD net-2 distribution and now 4.4BSD lite. I prefer NetBSD 
over linux on PeeCees, your mileage may vary.

> Second, which will be released first?

 MacLinux is big-time vaporware, supposedly released Jan-Feb. MacBSD
has been out for a long time.