It will depend on no of days for your trip.If you are planning to visit from delhi then options are:
1. Neemrana fort in 1 day 2. Jaipur, ajmer pushkar in 3-4 days.
3. jodhpur jaisalmer in 4-5 days.
4. Udaipur-mount abu-kumbhalgarh fort/Rankapur jain temple/Chittorgarh fort in 5-6 days.
Jaipur or Udaipur is best place for this time weather is changing rapidly so no to Jaisalmer and Jodhpur for this time.
These two places JPR and UDP takes 4-5 days to explore.
Best time to visit Rajasthan is in winters (December and January)
At this time it's best that you visit green Rajasthan instead of desert. 1 Jaipur 2 Udaipur 3 Mount Abu 4 Pushkar and Ajmer