Any reason you are definitely choosing a Boss?
Not that I have anything against them, but I was looking for a straight forward digital delay a couple of years ago and went for the Guyatone MD-3 over the DD-3.
Size and sound are just great.

What I love bout Boss delays, more so than the Guyatone ...

I love my DD3, and I managed to get it second hand for about £50 (thanks Progrockabuse). My bandmate has a DD7 though and I think it may be worth the extra cash if you can find one.

Why the DD7 then? I'm kinda a bit weird bout things, I don't like having pedals with features I don't use, and ...

I've got about £100 to spend, wanna have it out on the eBay shizzle, been fancying a Boss digital delay. Used to want a DD-7 but now it's all about the straight up digital delays, and narrowed it down to:

DD-5
DD-3
RV-3 (this is because at the same time I'm sick of the Behringer Reverb, it's ok ...