In our opinion wooden doors look better varnished and the finish tends to last far longer than painting.
We do offer a finishing service but it adds considerably to the cost and involves three of four trips to your home after initial fitting on dry, non-humid days. Many of our clients find this to be inconvenient as the dry days that fit with our scedule tend not to gel with their own scedule and once the wet finish is applied the door cannot be closed for 3-7 hours.  
We recommend that you set aside a wekend or a couple of days off work and finish the door yourself.
A guidance sheet will be given to you upon hand-over and it's really quite a soothing process not to mention very rewarding when you see the finished job