I have both and I can say that I tend to grab my Speedy more often. It is so lightweight and holds a lot (I have Speedy 30). Trevi is gorgeous, but heavy compared to Speedy. Get Speedy first and then Trevi.
I was trying on my cousin's ebene Trevi a few weeks ago, and I fell in LOVE with it!!! I decided that I HAD to have an ebene bag.
But I ended up getting the ebene speedy. The Trevi is soooo pretty, but I didn't think that it looked like a good casual, throw it on with jeans or yoga pants kind of bag like Speedy. I'm a stay-at-home mom, so speedy is more my style. Although if I had a job where I dressed professionally, or spent more time in nice clothes, I would DEFINITELY have gone for Trevi!!
I have both and although the Trevi can get heavy I reach for it much more then my ebene Speedy. I just love my Trevi because I think it looks so classy. I can wear it to work dressed up, and I wear it on the weekends with jeans. I have also gotten a lot of compliments on my Trevi.