I use a vest when I'm fishing most of the time. Mainly because that's what someone bought for me. I love it, it has a lot of space and carries everything I need. However, when I fish the park more this summer, I plan on either just carrying some sort of fanny-pack or a backpack in case I want to bring along lunch or some special equipment (extra shoes, rain jacket, that sort of thing). I like to keep it light when I'm hiking up and down streams. Tippet, extra leader, frogs fanny, nippers, box of nymphs, box of dries, water, and a can of dip and I'm good to go for mountain day trip.
The packs may be a little cooler (as in temperature, and perhaps in appearance too, its subjective), but besides many more advantages, I'm not really sure. They both provide ample storage and make fishing easier than just having everything thrown around and mixed together. A lanyard isn't a bad way to go either, especially for mountains or pond fishing. Stick a box of flies in your pocket, and on your lanyard, keep tippet, hemostats, nippers, and some flotant, and you're good to go for small adventures.
"I've got to stop wishin, I've got to go fishin"