All this exams are of same standards. But if you want to clarify then I would comedk will be toughest because you get 1min/ questions and the cut off goes really high. VITEEE is tougher than SRMJEE although this exams are much formulae based over concept based. All this facts are relative so don't focus on anything else except studying. Study NCERT and the books you use to follow, practice numerical and you can qualify in all the three with the same efficiency available.

I hope my answer helps. All the very best for your future endeavors!