Hi & welcome Stephen,
I would say it’s down to what you intend turning, if it’s just pens then a belt driven lathe is fine, if you intend to turn a wide variety of things then variable speed can be very handy.
Take for instance an out of shape blank with variable speed you can start slowly as you begin to true up the blank & as you progress you can slowly increase the speed until you are at the speed you want & the blank is true.
Personally I wouldn’t want to be without variable speed as it is so useful but as Mark & Colin have said it’s really down to you & your budget, best of luck in your endeavours what ever you choose.