Viscosity is way better than Cisco’s VPN client.
Sorry I know this is an old article but I couldn’t resist!

My co-worker the CCIE did strongly recommend the use of Cisco’s VPN client, but if I was going to use IPSec I wanted something that uses the built-in IPSec “raccoon” driver from Mac OS X (whose BSD subsystem is, of course, derived from FreeBSD). I’d also heard numerous horror stories from people who’d run into problems with the Cisco VPN client causing stability issues on their Macs. For that reason, I preferred not to use the Cisco VPN client and use a third-party IPSec solution at first. While my co-worker was very gracious in working with me to make a third-party client work, he did strongly recommend using the Cisco client. Good question, though!