We like our Culligan under-the-sink filter. It's got 3 large carbon filters and a reverse osmosis filter. It does depend somewhat on what you want to filter out, but the filter we have filters out everything. The carbon filters get out chlorine and any kind of organic hydrocarbons and the reverse osmosis gets out things like calcium and magnesium, the larger molecule non-organics (the things that make your water "hard"). I would recommend getting something that will filter out everything. Even if you have your water tested, you may not know what might get into your water at some point down the line. If you are spending the money, get a reverse osmosis filter. Our set-up cost about $800. That was a few years ago so it may be more now, but through Culligan you can finance it, usually 6 months interest free. The RO filter lasts about 10 years depending on how hard your water is and the carbon filters need to be changed once a year. They are about $30 for all three, I think.
I can't believe we waited as long as we did. I never drank enough water before because it tasted sooooo bad, now I guzzle it and so do my kids. It tastes good and I know it's clean.
I would also suggest looking in Consumer Reports and research it. There are probably new ones since we got ours.