I can recommend Kaiser. very modular, you can change and modify nearly every part. It is no problem to install a taller column or larger base board if you decide to print larger. You can easily convert an s/w enlarger to color or multigrade. As the system has stayed nearly the same since 30 years or so, it is no problem to use second hand parts to upgrade. They are also very well made. The 6000 series is suited for 35mm and 6x6. Second hand enlargers are so cheap nowadays ...
You should also look for a Rodagon or Componon lens, which do not cost a fortune any more on the used market these days.
Best regards, Benjamin