The more transparent the sealant, the faster it breaks down because it won't have as good UV protection. It's like the difference between a little sprayed on sunblock at SPF 15 and using the white zinc paste - the zinc paste is technically superior because it is solid and opaque and blocks the UV better than the stuff that rubs in and disappears on your skin.
But if you are willing to reapply more often then you can go with the transparent and let the wood's grain show through. Giving the deck a good cleaning once a year minimum is also important to prevent stains and inspect it for water damage and any other issues.
It boils down to how important the overall look is to you (and if you're willing to do the upkeep t keep it looking good).
I use semi transparent on my crappy wood deck (it's just treated pine or something?) and have to reapply it about every 2-3 years (super hot/sunny and rainy in my area so it tends to need reapplication much faster in that types of exposure). I think about the time we'll be readying the house to sell I'm going to switch over to the opaque stain, since the wood has still weathered slightly unevenly over the 12 years I've had it, (if you have rugs or furniture in specific spots, the deck will weather differently obviously) so I want to get it back looking more uniform.
