Originally Posted by Akubra
The 16x19 will give you more spin. The 18x20 will give you a slightly more consistent response from the stringbed. Depends where your strengths lie and whether you want to exaggerate your strengths or minimize your weaknesses.
Open pattern provides more power ( more spring in the string bed) and dense pattern has more control. Correlated to this is that the open pattern swings a tad lighter/faster/ more maneuverable than the dense pattern. The dense pattern is a tad more stable.
The 16x18 is more versatile (more popular) choice in general. It is the safer purchase. But between the 16x18 and 18x20 it's as close to splitting hairs as you will get in the selection of racquets. They both play very well and I interchange comfortably between the both of them.