Clipless pedals: Why clipping in so darn difficult?
This is part comment, part answer, but too long to fit in a comment, so here we go.

Personally, I use SPD, and when I ride with a group, everyone else has SPD-SL or LOOK.  I'm usually clipped in and across the intersection before they're clipped in.  Either I'm just really good at clipping in, or SPD are designed to be easier to get clipped in to. Even the very experienced riders tend to have problems with clipping in from time to time.  

Personally I don't know what advantage SPD-SL offers over SPD. People say that the larger platform allows for better power transfer, but I don't see how that makes difference. The foot pushes on the hard sole of the shoe, and sole of the shoe pushes on the pedal, which is made of rigid metal. Assuming there is no flex in the pedal or the sole of the shoe, it doesn't matter how large the attachment point is. 

Personally, I would recommend you try out a pair of SPDs. Borrow some from a friend or see if the shop has a demo pair and see if that works better for you. Too many shops will push you towards road pedals (either SPD-SL or LOOK) because you're riding on the road, and you will break "Rule 34" if you use mountain pedals on a road bike. I think that SPD pedals are a much better solution unless you're an actual road racer and only plan to unclip at the end of the ride.