Yes there is a difference. The Eris has a 3.2 inch screen, no physical keyboard, and the screen resolution isn't as high. The Eris also is made from plastic, which means it lighter. ANNNNND The Eris is running the 1.5 OS. (Motorola is running the new 2.0).
Now, don't get me wrong, the Eris is an excellent phone and will do all you ask of it.
It comes down to this, YOU! 
Go into a VZW store and play with both phones. Set aside an hour or so to do this. You need to see which phone meets what you like in a phone.
One more thing, the first app you download needs to be an anti-virus. There are serveral that are free and do a nice job. Since ANYONE can write and app and post it to the Android Market, it's well advised to protect yourself from malicious software just like you do with your computer.
Happy Holidays!!!!!!