As r.j.s points out, both products currently have huge problems. What you will find is that PocketMac constantly crashes for a lot of people and fails to keep changes that are made on your blackberry. MarkSpace/Missing Sync has a serious bug where it is randomly deleting contacts from the Mac address book. I spent much of the weekend scouring the Net looking for a solution, only to find that it is a problem that many people are having.
Who knows when RIM will get the new Mac software out (last I heard they are shooting for June). I would suggest you try PocketMac first, since it is free. If that doesn't work, get Missing Sync. Just make sure you back up your address book constantly, or perhaps set the options to always overwrite what is on the device (meaning if you want to add/edit contacts you have to do it at your desk). The calendar, tasks, iTunes, etc. still seem to work properly in Missing Sync.
Generally, Missing Sync has been very good, except for the current bug that seems to have coincided with the Blackberry OS upgrade (to 4.5).