I feel the safest is Ruprekha and Rex, they really can sing different types of songs and both are expressive. I dont think Shamit is at all a good singer. IF he selects tough songs and slips and can sing easy numbers only with ease what sort of good singer is he, Arijit is 1000 times better than him. Shamit chooses tough songs and cant handle them. Atleast Rex, Qazi they are untrained and they know what they should sing, they never try things what they cant. But Shamit he chooses a tough song coz he feels he is very learned and then his face becomes strained, vocal cords and nostrils swell, he tries to cover that up by movements and ultimately ends up huffing and puffing and shouting. Arijit, Arpita and Ruprekha are lot more versatile than Shamit and ohhhhhh yes the new guy Sandeep can really give him some competition.
Qazi he is a total popstar package with bit of everything in him and will handle those sorts of songs pretty well and Rex and Sandeep are good for both playback and pop numbers, rest all others are fit for playback and not stage performances. And I really doubt Shamit can handle a very tough playback properly, Arijit is far far better than him in that tooo.