I think it depends on the baby. Dr Browns are one of the more expensive types, but they can make a huge difference if you have a colicky baby. They have their downsides though - you have to learn how to keep from from leaking too much and usually get a few mild scalds along the way! They are also made up of 6 parts, so are a pain to sterilise and assemble.
For a baby without problems, my recommendation is for tommee tippee CTN. They have 4 parts and the teats can be assembled into the ring before sterilising. They aren't too expensive either, and don't leak unless you have the valve at the bottom when feeding. The only minor downsides are that you have to squeeze the valve open occasionally (the teat collapses if it sticks shut), and their variflow teats are very delicate, and have a tendency to split.