CrystalDiskMark is a synthetic benchmark that tests both sequential and random small and mid-sized file transfers using incompressible data. It provides a quick look at best and worst case scenarios with regard to SSD performance, best case being larger sequential transfers and worse case being small, random transfers.
At this point, we're probably starting to sound like a broken record, but once again, according to CrystalDiskMark, the Samsung SSD 840 EVO series of drives are top performers, regardless of the specific test. From 4K transfers at high queue-depths to large sequential transfers, the Samsung SSD 840 EVO series led the pack.
We didn't include RAPID scores in the graphs above, because they would have skewed the results significantly. Here's what you can expect to see using CrystalDIskMark's default settings over a small span of the drive.