I'm a hard copy person, so for me it would depend on where I'm going and what I plan to be doing. When I'm in the States, I go mobile because I don't pay for the data (well, it's not free, but I have unlimited with AT&T). Overseas I get a small pocket-sized guide. Especially in places like London I know even locals walk around with a dog-eared A to Zed of the city in their bags (so you might not stand out as much as you'd think - of course, YYMV). I download online stuff like mass transportation maps and guides (like the London Tube maps or the Paris Metro map) that I can access offline before I go.

If I'm just going to a beach type resort (which for us is rare) I'll download an electronic guide/book. If it's hiking it's going to be a hard copy because I'm not about to rely on cell phone signals or the ability to recharge my phone depending on how remote we might be.