Hey Manish,

Congratulations on qualifying JEE-MAINS.

Regarding all. Ive heard Thapar is a good option. I have lesser idea about Lnmit. But another thing is Thapar is bit expensive compared to other. But overall I'll recommend go for Government College Ajmer as it's about mechanical placements are pretty same for core Branches every where. 

Here is a link you can try to predict your College

https://engineering.careers360.com/jee-main-college-predictor?ici=search_trending

Best of luck