which is the best online class for GATE for mechanical engineering student?
There is no class that covers whole of mechanical gate topics. The GATE syllabus is adapted from engineering syllabus. So apparently you should not have any difficulty if you studied properly for your time in engineering. But I assume a general case.
The best overall help could be NPTEL. You can find lectures on different topics in Youtube under NPTEL. You can also get notes on pretty much everything from NPTEL app. These are few useful youtube channels.
Heat and Mass transfer (Professor Karthik),
Vibration (Gate academy)
Fluid Mechanics (Tutorials point)
Dynamics of Machinery (Education lessons)
You can find help from archive.arg too. To have good grasp of the topics you want or have to study, these sources can be of huge help.
Hope this helps.
You can visit many online websites for tutorials for preparing the GATE.
I would like to advise you to refer to a few youtube channels for the same. Also make sure to go through more previous solved papers . And the previous paper link is given below.,
Hope this helps you...