If it is within your means to obtain the Motorola Droid, obtain the Motorola Droid.
I used the HTC Hero before the Droid came out, which is the same as the Droid Eris. As a former Blackberry-user turned iPhone-user turned Blackberry-user, if I was going to use another touch screen smartphone again, it needed to be superior. I found that the HTC Hero/Droid Eris didn't perform up to snuff at all.
Running Android 1.6, I found the Hero/Eris to be slow once I had loaded some apps on it. Some people say they don't notice any sluggishness, but in that case I want to know what kind of phones they are used to. Perspective is everything, and being a former iPhone user, I needed the best.
Even worse than the sluggishness was the touch keyboard. I am pro-touch keyboard, and after typing on the iPhone keyboard, I actually preferred that to a physical keyboard honestly. I found the Hero/Eris keyboard to be extremely annoying. It wouldn't figure out words I was trying to type, and it couldn't even guess simple dictionary words that I was typing for correction. With these two things, it was a wrap for me, I had to get rid of it. The best part of the HTC Hero was the Sense UI, but if it doesn't run up to par and I can't type on the thing, the cons outweigh the pros big time.
When I finally got the Droid, I liked it a lot but given that the Hero/Eris was my first Android experience I was extremely skeptical. Yes it was bulky, but I've had a number of phones over the course of my life that seemed heavy compared to what I was used to, and I find you get over that pretty quickly.
If you're going to invest in a phone like this, you need something that will stand the test of time. The processor speed is good enough where you're probably not going to need to upgrade once your contract runs out. For me that's extremely important. With Verizon, once you're locked into that contract, you have a hefty $350 fee to pay to get out (I think it decreases month to month by like $10 bucks) and you don't want to be stuck with a phone that isn't up to par within a year.
In addition to the processor, the screen is beautiful. The touch keyboard is head and shoulders above the Hero/Eris (though it doesn't touch the iPhone), and you also have a physical keyboard as a backup if you prefer that.
Moto Droid all the way.