Some corrections here:
1)Strength of MARCOS is classified but rejection rates aren't as they differ year after year.They can range from 80% to sometimes above 90%.The other BS that not even family members like wives know that their husband is a MARCO is laughable now,this happened in the 90's when the force was just created now it isnt do,I have seen pics of kids of MARCOS officers running the MARCOS obstacle course in vizag and firing MP-5's.It is Navy media policy that MARCOS are to keep their identities secret.
2)SFF is the special operations unit of the R&AW it was till mid-80's that it comprised entirely of tibetians,since the focus is more on counter-terrorism than China SFF are comprised of people all over India,you have to be with the R&AW and pass the training at Chakrata.
3)Probably the most secretive group is the Special Group comprised of the best of SFF,Para(SF) and some MARCOS,it is probably India's Delta Force and its military designation is 22 Special Forces.This unit comes totally under R&AW and the cabinet secretariat.This was the first unit in India to use Tavors since their amazing relationship with R&AW they can get their hands on the best equipment they can.Major Udai Singh of 1 Para(SF) was a part of the Special Group.below is a letter from the C/O of Special Group to Maj. Udai Singh's parents:
http://majorudaisingh.com/letters/thapa.jpg
4)Garuds may have longest training period but that doesnt translate to supreme excellence ,In all army SF units around the world after selection/probation/assesment continuation training takes place for about a year and then courses like signals,close protection,combat diver,recon,sniper courses take place for the army SF folks periodically.With Navy SF it is mostly 2 yearS.Garuds have a totally different function that is to protect IAF installations and lase targets.Behind enemy lines,counter terrorism work is still left to the Para(SF) and MARCOS.