Which course should I pursue after completing my Diploma in order to get a good job, BE, B.Tech or AMIE (mechanical)?

If you are a diploma holder then AMIE (mechanical) is best for you, it may give you the chance to get good job with handsome salary.

According to my point of view, you should choose AMIE with mechanical engineering and if you continue your studies then you can choose M.Tech with polymer which is totally different from private B.Tech colleges.

B.Tech has lots of flood now. At this point of time the best strategy would be to follow the unbeaten path. Go for some unique course. You will not have to face a lot of competition.