Bit of column A, bit of column B. Carson did extraordinarily well in the early money game, but I think the cash spigots have started to dry up after all his gaffes.
I'd say the serious contenders at this point are Trump, Cruz and Rubio. Jeb may hang around for a long time though, just because he has cosmic fucktons of money in his SuperPAC and still a fair amount of establishment backing. The degree to which that backing starts to migrate to Rubio will determine Jeb's longevity.
Worth noting that in the latest NBC/Wall Street Journal poll, not only is Sanders polling better head-to-head against GOP candidates than Hillary in the early primary states, in most cases it's a race flip as a result:
Iowa: Trump vs. Clinton Clinton 48, Trump 40 Clinton +8
Iowa: Trump vs. Sanders Sanders 51, Trump 38 Sanders +13
Iowa: Cruz vs. Clinton Cruz 47, Clinton 43 Cruz +4
Iowa: Cruz vs. Sanders Sanders 47, Cruz 42 Sanders +5
Iowa: Rubio vs. Clinton Rubio 47, Clinton 42 Rubio +5
Iowa: Rubio vs. Sanders Rubio 44, Sanders 44 Tie
New Hampshire: Trump vs. Clinton Clinton 45, Trump 44 Clinton +1
New Hampshire: Trump vs. Sanders Sanders 56, Trump 37 Sanders +19
New Hampshire: Cruz vs. Clinton Clinton 44, Cruz 48 Cruz +4
New Hampshire: Cruz vs. Sanders Sanders 55, Cruz 37 Sanders +18
New Hampshire: Rubio vs. Clinton Rubio 52, Clinton 40 Rubio +12
New Hampshire: Rubio vs. Sanders Sanders 50, Rubio 41 Sanders +9
The good news out of all that is that Trump looks to be the weakest candidate in the general election, and simultaneously the most likely GOP candidate at this point.