Saunders was the original import of the LPL enlargers in the USA, but it switched to Omega/Satter quite a few years ago, so they are now sold as Omega/LPL. If the enlarger you are considering is marked Saunders/LPL, then it is either NOS (new, old stock) or used. The MXL is, to my knowledge, the current design of the 670 series.
You can find detailed information on the LPL enlargers at:
http://www.khbphotografix.com/LPL/ but note that they give the LPL model numbers, and Sauders/Omega modified the model names--both are shown.
If I were buying new, I'd certainly go with the Beseler 23CIII, or more likely the 67XL, as either is considerably less expensive by at least $1,000 US. Used, would depend upon the condition of the enlargers available.
The LPL is extremely smooth in its operation. The elevation is almost perfectly counterbalanced by a coil spring, so it doesn't take any effort at all to lift or lower it, except the weight of your own arm.
LPL lens boards are threaded, so no retaining ring is needed to mount a lens, Beseler lensboards need a retaining ring. Also, the LPL lensboards are round, so they can rotate. Nice if you need to position the lens to see the f-stop; on the Beseler, you need to make sure it's positioned right when you mount the lens. Also, you need to have a separate lensboard for each lens with the Beseler; since the LPL is threaded you can just screw in different lenses on the same lensboard.
Of course, one of the biggest differences is that the LPL is designed for 6x7 max, and the Beseler will do 6x9. I believe the LPL can handle some 6x9 negatives with the glass negative carrier with the masking blades removed, since the opening is about 82 mm wide, and many 6x9 cameras actually produce an image about 56 by 82 to 84 mm.
You really won't go wrong with either of these enlargers.