The fastest one in the toolshed is hisat2 (the wrapper is just called "hisat" if I remember correctly). For the "most precise variant caller" I can't really say, since that depends on settings/filtering. Freebayes is pretty good and available in Galaxy. I don't know what the state is of the GATK wrapper. That'd normally be the "go to" variant caller, but the licensing and downloading annoyance make it a little more difficult for proper Galaxy integration.