personally I'd go for the Strand location. It's much more central for attractions. Park Lane is nearer to the museums, Harrods, Knightsbridge and Kensington.
Both are excellent locations and there really isn't much in it.
I'd go for the strand too, it's on the doorstep of Covent garden, Leicester square, regent street etc etc, park lane is fine but it's just not as close to so much, although I'm sure the views across Hyde park would be fab!