The games are developing better technologies, but, EB still has the same system they did back when they began with a few updates here and there. EB needs to build a whole new verification and security system with better features in order to be competitive with Steam and VAC. At least VAC now went to VAC2 and they are currently working on VAC3. PB's UCON is still they way it has always been. There is no UCON2.
Punkbuster Pros:
Live banning
Global Bans on some violations (Should be all violations)
UCON system to allow streaming to 3rd party sites
PB Screenshots (When they work correctly)
CVAR scans
MD5 scans
Demos on some games (3rd party sites only)
Punkbuster Cons:
Kicks players for using non-cheat software like steam and xfire.
Black Screenshots
UCON not secure enough
PB GUID's can be spoofed(ET players)
Same GUIDs for different games (i.e. BC2 and MoH)
Can lag server with wrong configurations
PB kicks players if it can't communicate with EB
Auto-Updating does not work all the time (Have to manually update)
Some cheats that are supposed to be detected, aren't!
VAC Pros
Mass Bans
Auto-updated through steam
If you're banned, then you're banned from all games using that engine.
Once banned, you need to buy a new game.
No kicks for non-cheat software.
No lag from VAC
Now has VAC2 system
Has verification system to see if game is cracked or not.
More secure
VAC Cons
Have to wait for players to be banned (delayed mass bans)
No screenshots
No MD5's
No CVARS
Cannot contact VAC to discuss ban or to submit cheats via email
Does not detect some private cheats at all because they don't buy cheats.
Maybe some of you can point out other pros and cons for each. That is what I can think of at this point.