I've used a Beseler 67C since I bought it new in the 1970s. If it is one like mine, it has a massive single girder, and mechanics that withstand the moving process better than many (although Claire is right - stationary is better). It is limited to a maximum negative size of 6x7. It was originally supplied with all necessary condensers, so unless someone has discarded one of them, it can handle everything from Minox to 6x7, with the appropriate carriers and lenses. The current models use the same carriers and lens boards, so there is no shortage of same. There are also colour heads available, and probably variable contrast heads too (I've never seen one of those separate from a new enlarger). You can get parts, and can talk to people at the factory too!
A Beseler 23C series enlarger adds the ability to use 6x9 cm negatives. They are bigger, but plentiful on the used market, because they are well suited to schools and group darkrooms. Most of the same observations apply to them too.
Unless you need to go larger, both are good choices.
Matt