I blend in without even trying - not that you would know it if you saw me. I'm 6'2", with the strength that comes with it, and usually have an amorphous explosion of brown hair perched on my head. I'm not particularly shy or soft-spoken, and yet I've always been able to go unnoticed. I once walked behind two people who were having a conversation about me for 3 minutes, without them realizing it. I'll speak up in a conversation and people will jump up because they thought I was in another room. Chalk it up to body language, soft footing, crazy luck, or whatever, I have a tendency to blend in, which can get old at times, but is fun at others.
Given the choice, I'd probably pick blend in most of the time, because I tend to be fairly observant, and can enjoy sitting back and watching whatever's going on go on.
The exception is if it's any kind of discussion, debate, or argument. I LOVE to argue/debate. I get an adrenaline/endorphin/whatever rush when I argue, that's how much I love it. Screw blending in when there's disagreement to be had. Polite disagreement, of course, I don't get a kick out of ruining anyone's day (quite the opposite), but it's perfectly possible to have a casual discussion over the finer points of... whatever. And I love it.