I've defended Jadeja's ODIs selection on here before - I think he's a bit under-rated - but I don't really see what value he offers a T20 team. The bowling of the likes of Raina, Yuvraj etc is just as effective as his in this format and his batting is unsuited to it. And to add to that, he hasn't even been playing in the IPL due to a ban.
I like to have a side that can attack both with the bat and the ball. So if I can, I prefer to play a decent bowling all-rounder at #7 (esp if you have a good batting order from 1 to 6 and decent lower order batting with guys like Bhajji, Zak and Vinay, who can swing the bat well).
Now which bowling all-rounder to play at #7? A spinner or a medium pacer? Let's look at options:
For the medium pacers, Irfan Pathan (IP) comes off as the front runner and he has been batting well too. But his bowling doesn't inspire much confidence. Moreover looking at K11's performances, I would be tempted to not pick anyone from that side as I believe they have lost confidence (shown by messing things up at crucial stages) and probably need a long rest. Which is why I have left Yuvi (whose performances haven't been that good) and Chawal out too
For the spinners, we have Jadeja and Yusuf Pathan (YP). Jadeja is more of a bowling bowler while YP is more of a batting all-rounder. YP's bowling doesn't inspire much confidence and on top of that we have 'better' (arguably) off-spinning options in Bhajji and Sehwag. And similar to someone like Rohit Sharma's. If I am picking a bowling all-rounder to bat at 7 then Jadeja is a better pick. Moreover Jadeja also delivered with the ball in the high-scoring ODIs against SA (so he is not in bad form). And he is not that far behind in terms of bowling than other spinners like Ojha, Kartik, etc
So it is b/w Irfan (IP) and Jadeja for the bowling all-rounders' spot. There are pace bowlers who are bowling a lot better than Irfan is at the moment, while there isn't a big gap b/w Jadeja and some of the other spinners so I would pick Jadeja!
Now you have 3 in-form (relatively) pacers (from the options available and you aren't compromising on bowling by picking Irfan and using him as the 3rd seamer), a specialist off-spinner in Bhajji, who can swing his bat too and a bowling all-rounder in Jadeja, who is not that far behind other regular spinners and someone who bats decently. This combination allows Ind to go in with a balanced bowling attack (and a balanced side). If some of them are having an off-day, we have good part-timers in Sehwag, Rohit and Raina to support
This is how Jadeja adds value to the side. Ofc since T20 is dynamic, the combination could change depending up on form (and/or situation) but I would start out with the combination I listed in my last post
