I've watched a number of far more experienced pilots landing the B738 in moderate crosswinds and reckon the most commonly used technique is the sideslip as described in the FCTM. If I see the de-crab in flare technique on the line it invariably involves a late flare and very firm touchdown, especially on a wet runway.
Whaat? Where do you fly?
The smoothest possible landings on the 737 is when the runway is a bit wet. I presume it's because it delays the wheel spin up a bit + allow for a slight drift to go unnoticed.
To achieve a smooth touchdown in 737NG in general, you
have to de-crab during flare. I can't tell you why, but the NG will punish any sideways movement with the familiar rattling of anyone/thing onboard - no matter how low your rate of descend is when touching. This also includes a 5 knots crosswind. De-crab during flare technique can also be used even if the wind is calm to correct a slight error in the alignment. If you just put in rudder to align the nose and don't lower the wing a bit simultaneously, you create your own drift.
Landing straight is the key element to making smooth landings in the 737NG, which is a bit tricky aircraft when it comes to making greasers. Any sideways movement and the landing is ruined.
The classic on the other hand will allow a fair bit of drift to go unnoticed.