The first thing I look for when I'm checking out hiking boots is whether or not it's waterproof. This is essential. I have been in watery muck in England, snow in Virginia, and a muddy lake in Scotland on various hikes, and without waterproof boots, I would have had to turn around. I don't want my hike to get cut short over something so simple.
The second thing I usually look for is if it's over my ankles. This is for a couple of different reasons. The first is that I've been on many hikes where the rocks and other trail debris could have easily caused a strained ankle had my boot not been high enough to offer a little extra support. The second is that in all of those places I've hiked and needed a waterproof boot, they wetness came up over the top of my boot. Because my boots are ankle high, I have a little extra wiggle room in how deep something can get before it's actually a problem. I do know some avid hikers who opt for a lower profile, and it works just as well for them. This is a matter of personal preference, but it's something to consider.
I am typically brand loyal when something works, because I know how frustrating it can be when it doesn't. Merrell's hiking boots have never led me astray. My feet have never gotten wet on any of those hikes. When my old ones die, I buy new Merrell's. They're just a good solid boot, but without being too rigid. The sole is sturdy, and grips well.
If you're just starting to get some good hiking gear, and need some boots, I'd look into waterproof Merrell's. If you're hiking in any watery muck, snow, or muddy lakes, these will work fantastically. I very highly recommend.