If we're talking pure wicket-keeping, I'd put Taibu well up. I used to have a read 'downer' on Gilchrist as a keeper, but since England included Jones in their test side, I realise that the Aussies don't know how lucky they are (or rather reading this thread they do). His batting is such a huge bonus though, if he dropped a catch an innings he'd still be in credit.
Chris Read's a far, far better gloveman than Jones and if he doesn't start in the Ashes it'll be a travesty
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McCullum, Sangakkara, Boucher are all much of a muchness.
So, if push comes to shove, on pure keeping ability, Taibu top and you take your pick over the next four. If you include batting prowess, Gilly by a fair way. If you allow players who are currently 'resting between call-ups', then Chris Read takes it - just.