RC4-128 is weaker encryption than 3DES-168
AES is stronger than 3DES and faster. Both the Cisco concentrator and the IPSEC client support AES
I strongly urge you to use the Cisco VPN client over the Microsoft PPTP client because you have full control over the Cisco client, the user has full control over the Microsoft client behavior.
It is not just the strength of the encryption that is at issue, it is the
authetication process and the weaknesses of the authentication methods.