One's a better Keeper and one's a better Batsman...is that a fair assessment?
Certainly Alsop is the better batter.
To be honest, I've not seen enough of either's keeping to make a judgement.
The fact Alsop is presumably already in our one-day team might mean that he takes the gloves if Lewis isn't fit, so as to free up a space for someone like Ervine or Berg (remembering that Topley and Crane still need to come in, probably in place of Wheal and Fidel). Then again though, Dickinson did do well when he opened in the t20 last season.
That said, Lewis came out today in his usual position, and hung around for a while. So it might not be anything serious. What appears to be a bigger issue is Dawson's finger injury. He's become one of our most important white-ball players in recent years, and being out injured for any sort of length of time (like with Northeast) just rules you out of the entire one-day competition.