Express is just crap. Full Outlook is actual shit.
It's all on what you want, really, in a terrible, security-hole laden, unusable product that will manage your email more than you wish it did, and not manage it less than you would prefer.
I suggest skipping both and going with a good email program like The Bat! or Pegasus.
The Bat! is what I've used for years - no security problems, doesn't show HTML email (which eliminates a lot of problems) and it's so customizable, and so powerful, it will leave you speachless; and yet at the same time, it's very easy to use if all you want is basic email.
The Bat! can be gotten here:
http://www.ritlabs.comI've never used Pegasus, but I hear very good things about it, even from people on the Bat! email lists I'm on. I am a total evangelist for the Bat!, and I wish more people would go with it - it would eliminate all those damn forwarded emails with 900 headers on 'em, it would prevent a lot of security problems, and all my emails from people would actually thread properly, be formatted properly, and it would get people to stop using that damn HTML email.