I was facing the same dilemma. I like both sets. (Edit:WHOOPS!!! I thought you were referring to the fixed end sets that are so popular from tooltopia!) I'd go with the GW set you mentioned.
Pro's for the GW style:
Extra long which is perfect for access.
One end is forged. So no worrying about busting the ratcheting end.
Great price if you use the metric/sae bogo on tooltopia.
Cons?
Takes up more room in your box versus the multi-sized Kabo versions.
Doesn't have a flex end.
Pro's for the Kabo style wrenches:
Extra long for access.
Both ends have flex joints.
Both ends ratchet.
Minimal space needed in the box since each wrench has two sizes.
Cons?
You run the risk of busting the ratcheting end since there is no solid fixed end.
Warranty might be more of a possibility too b/c of the above reason.
By the time you buy both the metric and sae versions of these, you are well above the price of the tooltopia bogo price.
If you consider buying both, consider this:
With the money you spent on both sets, you could have just bought Gearwrenches 120XP set of double box wrenches in both metric and sae.
You'd save room in your box vs. having both styles of wrenches you mentioned. You would also have the benefit of the fixed/forged end like the earlier mentioned GW's, but with the added benefit that the ratcheting end has a flex-joint like the Kabos.
That's what I'll be doing once my taxes come back, buying the Gearwrench 120XP double boxed set.
Cheapest place to get them is on Tooldiscounter.com