Beseler 45MX, or one of the many variations. As cheap and common as dirt. Excellent workhorses. Allow lensboard tilt, which can be very important if you are using a camera with limited movements (i.e. movements in only one direction, like a Speed Graphic). I just got one with four German lenses on boards (Schneiders and Rodenstocks), four negative carriers, a color computer head, and a color analyzer for $220 all together. (Plus a timer, trays, and various other odds and ends.)
I love my Omega B22XL, I love Omega Ds (and I am stuck with my Omega F

), but I considered the Beseler an "upgrade" over the Omega for a reason or three other than its greater-that-6x6 printing capability. I work in a community lab that has about 40 of these workhorses, so I am pretty familiar with them, and I think they are the best bang for the buck in a used mid-level enlarger. I find the whole enlarger better built and more solid/stable. I find it easier to align, and that it holds alignment more solidly. I use the lens tilt from time to time as well, which is especially an issue for me with the larger medium format frame sizes and with sheet film, because I often shoot things that are particularly suited to the use of camera movements when I am using this larger film...and I fairly often shoot with cameras with limited movements (Speed Graphic, Mamiya Super 23).
This being said, I definitely would not recommend strongly against an Omega in any way! They are simple, beautiful machines capable of professional-quality results. I just find the Beselers to be a little more full featured and easier to work with, personally. If you find a good Omega kit for a good deal, take it. You can always switch later if the need arises, and with the market being what it is, as long as you do not overpay for the enlarger, you will not even lose that much (if any) money by doing so.
You can only go so small with a 4x5 enlarger, but being single-column enlargers, the Omegas do have a "slimmer profile" than the Beselers, if that is a consideration that your space dictates you honor. They also seem lighter (better for moving, worse for enlarging). If you break down and set up your enlarger frequently (as in removing the column from the baseboard), they are easier to break down and set up, but harder to store than the Beselers. Beselers have two columns to lean on, and are more stably balanced for storage with the enlarger body attached. (Just hang from two solid hangers, like 2x4, large dowling, etc.) Omega's design makes the column harder to store with the body attached.
It doesn't matter to me, but the Beseler tilt