The (2a) Plus launches a week tomorrow (Wed 31/07), so I would wait until there is further information and a price. The (2a) may be discounted too – or perhaps not, to make the Plus look better value.
If none of that matters to you (I doubt the two phones will be far removed from eachother) and you prefer the design of the phone (2), go for that one. Although I wonder if the phone (2a) Plus will include more stuff in the box.