I used to have a boss DM-2 back in the 80's. It sounded sweet. Depends on what you are trying to do though. I have a DD-3 now, and it sounds pretty nice too.
I was on the same quest as you. This one doesn't have the loop feature that the DD-6 has, but is very un-digital in terms of sound character. Echoes are pretty much the exact same sound as from your amp (ie without any added tinny qualities). Also has an INCREDIBLY long delay time if you set it on the long mode, is small and durable, and has no loading down (that I can hear) without being true bypass. You can find this pedal for about $100.
The DD3 and DD6 both have a looping feature I believe that you can record and repeat, but both are also infamous for being...well...digital. The reproduced sounds have full sound spectrum reproduction which is a little different from true decay in that the higher frequencies are preserved (which is why the echoes start to get tinny IMO). I think Analogman has mods for these pedals to cut highs.
The EH Memory Man is good, warm analog sound so it has its own unique character.
I own a Guyatone MD3 and would buy again if I had to, but if you're set on a Boss, get the DD3; the DD6 is trying to do too much, is overpriced, and has worse sound quality from what I hear.
I liked the reviews for the MD-3. But the complaints about the battery casing bothers me. I am still considering it though. I heard some sound tracks on musicanfriends.com and it does sound rich and warm.
I have the DD20 and like the amount of control I get with it. I posted a review on here about it a while back. I'm sure you can find it on a search if you're interested.