A condenser head uses an incandescent bulb shining through simple lenses (2 hemispheres of glass on my old Omega DII).
Brighter: shorter print exposure times
Sharper: the pro is obvious, the con is more problems with dust, scratches, and defects in the neg
Higher Contrast
A diffusion head uses an incandescent or fluorescent bulb/tube shining through a diffuser.
Longer print exposure times.
Less problems with dust, scratches, defects...
Lower Contrast
A dichroic head is similar to a diffusion head and uses high a intensity bulb and a diffusion chamber (a mirrored box) to mix the light with cyan, yellow, and magenta filters that are built into the head for color printing and variable contrast BW.
Any enlarger from one of the major brands will probably work very nicely. More modern designs will have more features. Make sure you get one that is big enough for future interests; a used enlarger that will do 35mm through 4x5 doesn't cost much more than one that'll only do 35mm.
I have an Omega DII and a Beseler 23C; both older than I am. I have a cold light diffusion head for the 23C, but I prefer printing with condenser set-ups.