I have four baby joggers. One is the Baby Jogger brand, the other one says "Dreamer Design" and the other one says "Instep." The last one has no brand name on it but it's a baby jogger that converts to a bike trailer. It's built like a tank and is designed for handicapped children. Insurance paid for it. I think it was $3,000.
In my favorite one (Baby Jogger brand), the seat is more like a sling--it's connected at the sides and there's nothing beneath it so you don't have to worry about padding. Also, it cradles the baby in a banana-hammock way and adds to the stability.
Test your baby jogger out before you buy. Some are very top heavy, which means the handles where you push wants to go down to the ground (front wheel comes up). If this happens and the handles hit the ground, your baby will probably be okay, but it's something to avoid if you can.
Test the hand brake. Good baby joggers have a parking brake (something that you set with your foot, usually, that locks the back wheels solid) and they should also have a hand brake which you'll need when running down hill.
I wouldn't take my baby on most trails before the age of two, but maybe I'm over protective. The trails I run on are pretty bumpy. Taking a baby down paved streets will be no problem. I have a double baby jogger and I take two of my boys (ages 6 and 3) in the woods every week almost.
I have a special handicapped baby jogger for my 13-year-old who is non-ambulatory. I run in the woods with her as much as I can. It's our favorite time together. She loves how bumpy the trais are.
The baby jogger people have been the best to deal with. They've been very willing to adjust anything I would ship to them.
Also, test how easy they are to break down, and how well they will fit in your trunk or whatever. My favorite Baby Jogger brand doesn't really break down at all (it's for bigger kids and not really babies), and so it's one more thing I have to deal with when I drive to the trails. I have to remove the canvas "sling" part where my child sits because it could be damaged by the wind if I put it on the luggage rack. So I remove the sling and just put the skeleton of the b. jogger on the roof with a couple bungee cords and it's easy to transport.
Most other baby joggers fold up pretty small, but some are much easier to fold than others. Be aware.
My advice:
Look at the stability (top heavy)
Test the brakes
Look at the padding
See how easily it folds
Check out storage (water bottles for you, snacks for child)
I've had joggers with big wheels and little wheels and I don't think it makes any difference. I thought big wheels would be better but that's not necessarily so.
The easiest way to turn a baby jogger is by lifting the front wheel off the ground an inch or two. It becomes second nature while you're running.
Garage sales are an excellent place to buy a good baby jogger.