I think it's hard to leave Morgan out. He's scored more hundreds than anyone but Tres, at a strike rate better than anyone bar a few other members of the current team, more sixes by far than any other England player, and a very healthy average to boot.
I know the modern game is skewed in favour of batsmen, but in terms of overall career record, I'd say it's only really KP and Root who could make a case for being a better overall ODI batsman for England. Trott has a great average, but his strike rate and conversion rate to 100s both aren't that good. And while Tresco and Gooch were very good, I think at best you could say it's a toss-up between them and Morgan, and too hard to compare between eras.
You also have to look at the impact on games. Morgan wins matches for England - he averages over 50, with 7 hundreds and 18 fifties and an SR of 95 in England wins. I'd argue only Root and Colly have had as much impact as matchwinners, in terms of proportion of their centuries and improvement on their career averages in wins (I didn't realise how much of a matchwinner Colly was as well until i looked up the stats just now. Should have known. And I'm discounting less than 500 runs in England wins as an insufficient sample
http://stats.espncricinfo.com/ci/engine ... pe=batting).
I've seen Morgan close out chases that I thought we were going to get nowhere close.
I'll grant you Gooch, but if Hales career fulfils its early promise I think he could edge out Gooch in a few years' time.
Tresco/Gooch/Root/KP/Morgan/Colly/Buttler/Flintoff/Swann/Anderson/Gough