Ignoring the condescending tone of a post and all the variance theories and what not, I think we should keep it simple. Cricket is complicated enough as it is without as making it even more complicated.
I don't really think the difference between the best and the worst players means much. The difference between Bangladesh's best and worst player might be the same as the difference between Australia's best and worst player, that doesn't mean Bangladesh = Australia. Or maybe I'm missing the point, maybe Prince EWS can help here.
The basic factor for me really is that in a test you have to maintain your standard and intensity for that much longer; in a T20 you 'only' have to maintain it for 20+20 overs. It is why the likelihood of an upset is more in a T20 than in the 5 day game. That, for me, is the clincher as to which format is easier. The longer it is the harder it is - you could extend the same logic for why a player averaging 50 over 50 tests is better than a player averaging 50 over 10 tests(all other things remaining constant)
However, what I'd like to add is that (and I already touched upon this in an earlier post), it would be too simplistic to say T20 blokes can't perform in the whites. You could make a fair case that more test players succeed in T20 than vice-versa, but T20 has definitely influenced the way test (and ODI) cricket is played. I am dead certain that a player like Maxwell if given a fair go will come up with at least a handful of match defining/turning knocks even in the whites. It has become a fashion to label and chastise Suresh Raina for instance and put him down at every opportunity; but in reality this is the same bloke who scored a ton on test debut and in his first match outside the subcontinent he even managed a 70-80 odd against what was then a very good English attack. Sure he's more suited to the shorter formats but he's not just a 'hack'.
As regards which shots are more difficult to play, it really depends on the player. As rightly pointed out, a Dravid may find the midwicket mow harder to play than Raina; but as a rule of the thumb, slogging is generally easier than 'proper' cricket shots. It is why a Dravid is more likely to give you a 60(40) in a T20 than Raina is to give you a 150 against Donald and Pollock in Jo'berg.
I don't really think the difference between the best and the worst players means much. The difference between Bangladesh's best and worst player might be the same as the difference between Australia's best and worst player, that doesn't mean Bangladesh = Australia. Or maybe I'm missing the point, maybe Prince EWS can help here.
The basic factor for me really is that in a test you have to maintain your standard and intensity for that much longer; in a T20 you 'only' have to maintain it for 20+20 overs. It is why the likelihood of an upset is more in a T20 than in the 5 day game. That, for me, is the clincher as to which format is easier. The longer it is the harder it is - you could extend the same logic for why a player averaging 50 over 50 tests is better than a player averaging 50 over 10 tests(all other things remaining constant)
However, what I'd like to add is that (and I already touched upon this in an earlier post), it would be too simplistic to say T20 blokes can't perform in the whites. You could make a fair case that more test players succeed in T20 than vice-versa, but T20 has definitely influenced the way test (and ODI) cricket is played. I am dead certain that a player like Maxwell if given a fair go will come up with at least a handful of match defining/turning knocks even in the whites. It has become a fashion to label and chastise Suresh Raina for instance and put him down at every opportunity; but in reality this is the same bloke who scored a ton on test debut and in his first match outside the subcontinent he even managed a 70-80 odd against what was then a very good English attack. Sure he's more suited to the shorter formats but he's not just a 'hack'.
As regards which shots are more difficult to play, it really depends on the player. As rightly pointed out, a Dravid may find the midwicket mow harder to play than Raina; but as a rule of the thumb, slogging is generally easier than 'proper' cricket shots. It is why a Dravid is more likely to give you a 60(40) in a T20 than Raina is to give you a 150 against Donald and Pollock in Jo'berg.