Well, I think, having sailed tons of sloops, the 18ht and the CFR20 that both rigs have their merits. The uni's are faster around the cans, BUT I think the grove for those boats is much narrower (i.e. less forgiving).
Uni is NOT faster. If you are limited in sail area like the A class, it is more efficient to put it all in a single higher aspect sail. If you are not limited a jib adds more power at a low center of effort and provides a slot for smothing the flow. There is definitely a reason all the Euro guys have put jibs on their M20s because it is faster.
Uni is easier to set up as their is only 1 sail, but that is pretty much the only advantage. Personally I feel the uni is more difficult to sail, but that is primarily due to my lack of time on uni rigs. If cost and sail area are not an issue definitely go sloop.
Matt
