I had an Beseler 45 (earlier version, bought used), a Zone VI-II, and finally a Saunders/LPL (I guess now it's Omega LPL).
No question, the LPL is the only one I'd buy again. It operates beautifully & smoothly. The chassis is spring balanced, so you can move it up or down with a single finger, and it just works right. At around $1500 new, discounted, for the 4500-II version, it's also the cheapest one. By the time you've added a condensor or diffusion head to the Beseler or Omega, they are $100 to $700 more.
If you get one the LPL, get the focusing extension so you can focus when doing big enlargements. Consider, too, the masking negative stage, as it reduces the chance for flare when cropping. I don't think Beseler nor Omega offer this.
As for the Beseler: this is a fine chassis, and the only one I know of with a focus lock. That's a nice feature. Motorized lift, but I don't miss it with the spring balanced LPL.
Zone VI had some problems for me: I had the VC cold light head (very nice) but it was hard to focus and compose, as the light is all blue & green. Big problem: there is no easy adjustment to tighten the focus friction, and on mine the lens stage wouldn't stay in place if the bellows were compressed too much. Finally, this is really a 4x5 & 5x7 enlarger only. It does not work well for medium & 35mm formats. For example, with 35mm you are wasting 96% of the light which falls on the negative carrier, but not the negative. Also the bellows don't compress enough to do small prints from 35mm. The enlarger has some good ideas, but on the whole isn't thought out thorougly.
You'll need to consider what light source you want: condensor, cold light, or diffussion. I've used all 3, and all work well. I've settled on dichroic color diffusion. Most color heads are diffusion, and these work fine for me for B&W printing, too. There are heavy opinions for diffusion (cold light) and others for condensor--I say ignore those opinions. Any of the heads make fine prints if you've adjusted your negative density to the light source.
If you're getting a new enlarger, go for the LPL if your funds are limited. If you're buying used, get the cheapest of them in the best condition.
The absolute BEST advise is: go to a photo store and operate the enlargers to see how they work for you. Some photo equipment, like cameras and enlargers, just seem to fit individuals differently--like clothes and cars. You really won't know until you try different ones. For example, LPL has 2 medium format enlargers. I like the cheaper, because the more expensive one had filter readouts that were much harder for me to see.
Good luck with your decisions.