It's doubtful if you will find anyone that has used both programs to give you a qualified opinion.
Like most, I've used Sygate Pro but cannot compare it to Outpost as I've never used the program. The only other software firewall I've used is Zone Alarm. I'm not qualified to give you an objective comparison. I don't care much for software firewalls as I run dual stacked routers.
Try doing a search for Personal Firewall Reviews. The results should be a bit more objective as it usually comes from someone who has tested the programs and is usually not one-sided.