i have a similar thread about this, been debating it in my head for awhile now and i think ive made up my mind... heres why:
i just spent about 2 hours at verizon messing with the moto droid (i currently have the eris) and i am not impressed
yes there's a lot of personal preference involved but, there's a lot other factors
they say the moto droid is so much faster, nah.. i didn't get that after using the eris for this long. as a matter of fact, the eris feels so much smoother (the SenseUI). i felt choppy on the home screen with the moto droid. that was my first revelation...
secondly, i held it, put it in my pocket, and it just didn't feel right, its a rectangular brick of a phone, ugly indeed.. the eris is sleek and sexy
thirdly, yeh the moto droid has a bigger SD card but do u need 16 gigs? your paying for it.
also, the web browser. the pinching of the htc is awesome, its more interactive and feels better than the simple zoom in and zoom out.
the slide out keyboard? some may like those, but me, no. i would preferably never use the keyboard because i hate sliders, they feel cheap and it's not my style (personal preference)
then i thought about the manufacturer, motorola... HTC is where its at, motorola is on a downslide while HTC is on the up.
now some may say "dont get either, just wait for another".. but the way phones are these days your gonna wait your entire lifetime to be happy. once u get a 'newer' one then another 'newer' one will come out and u'll be like damnit, why didn't i just wait.
in conclusion, HTC is going to fix these bugs that are littered around (and moto's got its own bugs to fix) and HTC is going to get a brand spankin new Android OS update which will be very interesting with the SenseUI. so if you want to spend the extra money on the brick phone, go ahead, but i really don't think you'll be satisfied if you think the htc eris is not your phone.
of course this is all my opinion, do what you will, but don't expect to be piss your pants happy when you get the moto droid, and when the eris update comes out u might be kickin yourself for not keeping it.
that is all