From my own experience the top of the tree is the Durst L1200, the biggest issue is because they are out of production, accessories ( mixing boxes, condensers and carrier masks) can be very challenging to find. They were available with 4 different interchangeable heads, color, B&W, point, and Multigrade
Durst CE1000 this is a good basic enlarger, but due to its age is nerve impossible to get accessories or parts for, if you buy one make sure you get a full set of condensers with it and a set of carrier masks
Next is the Durst 138 5x7 enlarger, you need to make sure that you get a good carrier with it as these are more often or not very worn, and a replacement can cost more than you just paid for the whole enlarger. Bulbs for this enlarger are normally very to get ....I managed to find a led bulb that fits and works like a charm. A color headband a cold light he’d were also available at a price......
De verge 504 ect these are normally very expensive, I think that you can still buy parts for them at a De vere price.....my experience is very limited but if the price is right go for it.
Chromega D series these are good enlargers but built out of sheet metal, not cast alloy like a Durst or a De vere, There were a lot sold so parts a quite available.
My advice is make sure you get as many accessories as possible with your enlarger if you buy used, the best ones are enlargers that have just been removed from production, or a darkroom that is being closed down. This way you are more likely to get all the accessories with it, stay away from junk dealers on selling enlargers as they properly did’nt get the accessories because they don’t know what they are selling.....they only pulled the enlarger out of the skip.
Sometimes you can get very lucky and get one from a school or education body that closed its darkroom and put it all in storage....everything in its original boxes still like new.
Hope this helps a bit
Johnkpap