It's quite hard to work out how England might line up.
Top order options
Buttler - I think he's best as opener. Struggles a bit starting in the middle.
Roy - Average record but is a selfless player with excellent s/r and has shown that he can destroy real pace bowling. Probably hangs onto a spot maybe wrongly on account of his ODI record.
Bairstow - Will be in squad definitely. Probably best opening but capable of batting in middle order.
Malan - Great record in internationl t20s, only left hander in the top order options. Average fielder and they can't carry too many of them. Doesn't quite hit the ball as cleanly consistently as most of the other options.
Vince - Will almost certainly miss out.
Banton - Probably going to come to soon given the alternatives.
Hales - England have probably moved past him given they have no shortage of options in the area.
Root - Contentious for sure. Goes well for England and maybe the argument against real high quality teams England may need someone who is not just trying to smash it out of the park. Also offers off-spin option as 6th/7th option which is useful given lots of the batsman in contention don't bowl at all. Still I think he's going to find it hard to get back in the side with England's approach likely to be to just go hard from ball 1 from everyone.
I think Buttler, Roy, Malan, and Bairstow likely to go. I can still see them possibly dropping Malan after a couple of failures; he does though have a big advantage of being the only leftie in top 3.
Middle order -
Morgan
Stokes - Poor record and his power hitting is too impacted by the strong bottom hand but is the heart of the team and excellent fielder. Will hope they can get the best of him when he gets a consistent run of games.
Billings - Can't see him making it. Just a bit too limited. Doesn't strike the ball well enough.
Ali - Will be there. Only reasonable offie to compliment the leggie. Power game has come on massively even if he does have some big troughs in form, and isn't great in the middle order.
Gregory - Strikes it well in county cricket but will have to show he can do that at a higher standard and im not sure he is good enough and/or will get the opportunity to show that. Bowling is meh in t20.
Bopara - The wild card. Probably the most experienced middle order bat they have and is never short of offers for his services across the world in t20. Still has the label as a bit of a bottler and England will probably be wary of going back to someone who never succeeded in the past.
Denly - I hope not. They want him to be an allrounder who bats in the middle order but he simply isnt. Doesn't have the power to bat in middle order. Not a good enough spinner to be an allrounder. Would want to bat in the top 3 but is lacking relative to the options.
Dawson - Maybe competing for Ali's spot but likely to lose out. Doesn't have moeen's wow factor with the bat and spins the ball the same direction as the leggie (although rashs bowls lot of googlies so less of an issue).
Morgan, Stokes, Ali and Bopara my options here.
The bowlers.
Archer - Offers the pace, yorker etc. Good strike bowler options and at death.
Jordan - Has been excellent in NZ. Really developed over the last year or so seemingly into a more reliable performer. Has the added excellent fielder/ useful batsman to his bow.
T Curran - Similar to Jordan in he offers good fielding/batting as well as his bowling.
Willey - A little unlucky to not be on this tour instead of S Curran who he will be competing for a spot with come the world cup. Has a decent t20 record for England where he regularly picks up wickets with the new ball. Is another really solid fielder with excellent athletism and decent tail end batting.
S Curran - Imo a little behind Willey on current ability. Very similar t20 cricketers.
Rashid - good record and trusted by Morgan to bowl to specific instructions.
Wood - Hard to see him being fit and unless he's bowling 92 mph+ consistently doesn't have the skills.
Parkinson - Interesting to see how he goes against international batsman due to his lack of pace through the air. Started well. Could be an option on some of the big grounds in Australia.
Pat Brown - Can't see them going that way. More rounded players available with more experience.
Archer, Jordan, T Curran, Willey, Rashid my bowling options.
Buttler, Roy, Malan, Bairstow, Morgan, Stokes, Ali, Bopara, Archer, Jordan, T Curran, Willey, Rashid + 2 more make up my squad so far.
(I couldn't resist going contrarian with the Bopara pick.)
