#15 I like the clean look - but you may not be aware of a US bank called TD Bank North (www.tdbank.com) whose logo is too similar to this. To be really picky, the T and D do not appear the same size.
I like #46 much more than #45 - it seems much cleaner without the colored background. The little shadow adds a nice bit of interest, too. It's also interesting because the top and bottoms of the T and D are NOT perfectly aligned. I'm just curious how that would look if this were even more pronounced? But I don't want the letters to become so abstract that they are difficult to recognize as letters...
I like both #56 and #57 very much. I didn't pick up on the negative s - thanks for pointing that out.
Just a thought - how would they look if the bottom of the D and the top of the T were each extended a little more? Sort of invading the other's space even more. But still recognizable as initials. Also maybe the company name a bit larger. Thank you.
#90 - I like this better with the longer "arms". Please see my general comment about a tag line, I hope you get a chance to make this revision. Thanks,