While both the areas are located in south east Jaipur, the return on investments is quite lucrative in a medium to long term ranger. As mentioned by the above user, if you are strictly seeking a short term investment property then Malviya Nagar offers a better choice as it is easily saleable owing to its central location to commercial centers and connectivity to the rest of the city.
Both Milap Nagar and Malviya Nagar have their pros and cons. It is difficult to choose one area from another. While prices in Milap Nagar are a slightly less compared to Malviya Nagar, the latter is considered to be more uptown out of the two areas
Speaking purely in term so short term return on investment for residential property, I would suggest you to go for Malviya Nagar. It is the more up fluent of the two areas and offers better scope for short term gains.
Malviya Nagar and Milap nagar are both located in south east Jaipur. You have not mentioned whether you are looking to invest in a residential property or a commercial one. Both Malviya Nagar and Milap Nagar have a blend of commercial and residential projects.