I have travelled in almost any season to Mahabaleshwar. I have travelled by car from Pune. You can also take a luxury bus from Pune leaving every hour or so. They are also neat.
Best time to travel is in rainy season. The climate is really good during that season. You actually travel through clouds while on road.
I would recommend MTDC resorts to stay. Only one description of these resort...’’Hassel free’’. You get good Jams and jelly sweets. If you go during winters...late Jan ..you can actually pick strawberrys from the farms.
Horse riding is not as enjoyable as compared to Matheran. Bit polluted than Matheran.