If money is an issue, the SD is a little bit better value for the money. The SD is a fine pistol and in situations I prefer it to all others -- it carries well (thin & not too large) and is completely reliable.
If money is not an issue (well, within reason) then the M&P might be the better pistol for you to start with, assuming you want a striker fired pistol. (The value there is that every trigger pull is the same. The down side is that they are not as crisp as a good SA/DA pistol can be).
The M&P is good value for money, and also very reliable. As a new shooter, you are going to be relating to other shooters and asking for ideas and trading impressions -- with the SD, you might end up at the short end of the range snobism thing that might take away some of the fun for you. (It doesn't bother those of us who have had a couple of guns, maybe even some expensive ones, and can put the value of the SD in context for the casual critic).
For a bit of heresy on the S&W forum -- if you are really looking for a SA/DA pistol with a very, very nice trigger, for a reasonable price, take a look at the SigPro SP2022. Of course, you don't get S&W's legendary customer service, in case you need it, and you don't get the consistency of a striker fired system. But they are nice.
Bottom line here, and I've gone on too long, the SD would be fine, but I'd lean towards the M&P. I bought my first M&P, then doubled back for my first SD...