To be honest, I believe the X360's LIVE service is very much more capable than the PSN, although Sony has been catching up. This is due to LIVE's maturity vs PSN's infancy in terms of development stages.

MS's LIVE platform is also streamlined and handled by MS themselves, as opposed to Sony who basically still lets developers handle the multiplayer components of their games themselves.

But speaking as a PS3 owner, I can tell you that PSN is very functional (for all the needs you mentioned) and I imagine it will only improve over time as they try to catch up with MS.

Just my 2 cents.