You can choose either of the two without any problem. This gives you the advantage of a larger number of plots to choose from. North facing properties are generally priced slightly higher as it is considered quite auspicious. Also any land with a better front is sold at a premium. If you are buying for an investment purpose, keep a medium to long term outlook to get the best return on your investment.
I totally agree with second the opinion of the above member. There is not much of a difference between the two areas. Both Shyam Nagar and Nirman nagar offer equal opportunity for land price appreciation in the medium to long term.
Since you are interested in buying land as an investment vehicle, you can choose the directions, plot front, vastu compliance and choose in either of the two areas.
Both Shyam Nagar and Nirman nagar are located in the north to northwestern region of Jaipur. The price trends for both areas are quite similar and the future appreciation is also quite synonymous.
I suggest you can choose either of the two areas and there should not be much of a difference. Chose the area where you get a better deal and comparatively better location.