If I had to make a lot of pegs, then drive them in to fairly hard ground.... I'm likely to pick a hatchet over a knife. Although I have to say that my military golok is heavy enough to drive pegs and I wouldn't mind hammering with the side of the blade. However, I could cut a decent baton club with my big sheath knife, then use the baton to help cut the pegs then drive them.
Safety is a big thing for me too. I've used tools a lot (I'm a metalworking tradesman) and I'm fairly well co-ordinated, but I am aware that great care is needed to make sure that the hatchet hits the target every time. It is relatively easy to miss and have a scary 'swing by' experience. Like Marcelo said, a full length axe is safer. I've fitted longer handles to hatchet heads, and I like the result. Maybe you could consider this too. You can get a decent swing going using both hands, and the overall weight isn't too bad for carrying long distances. And I've figured out that when I'm splitting firewood on a chopping block with a long-handled axe, if I keep my hands lower than the head of the axe throughout the swing, then I am more likely to be safe if the axe misses or glances off the wood.
For close-range chopping I think a big knife is safer because you have the length of blade and generally you are aiming to hit the wood or whatever with the 'sweet spot' of the blade which may be somewhere near the middle..... so unlike a hatchet with a blade that is only about 3.5 inches long, you have a blade which might be 7 inches long and less likely to miss. Plus a knife doesn't have the weight of the hatchet head at its tip, so even if you do miss the swing is more controllable. You have to be careful though.
And for chopping light scrub and small branches, a knife seems to work better than a hatchet (for me anyway). It has a thinner blade which aids penetration, and it can be swung fairly fast.
If I had to carry just one tool (which is seldom the case), I'd like to have a pointy cutting tool. One that can be used to bore holes, carve nicely, and get pushed into an animal should the need arise. A wild hog can be finished off with a hatchet, but I think I'd do it with greater confidence, finesse and efficiency using a pointed knife.
One thing I find myself using a knife for quite often is digging out splinters. A hatchet isn't so good for surgery like this.
I find that a knife is much nicer to carry.
If I had to choose between a knife and a hatchet in very cold wilderness conditions, I guess I'd pick a hatchet to ensure that I could cut branches for shelter and get a fire going. But a long-handled axe would be better.
You might not want to consider a machete, but I have found my 10" Tramontina to be very useful indeed. I ground the end of it to make it more of a pointy tool:
Here is one of my re-handle jobs using a cheap (but very good) hatchet head. It is a nice project to hack and whittle a strong handle from a tough branch then carefully fit it to the head. It may be a good idea to file the hatchet eye to even it up and to remove lumps and sharp edges. Old heads can be found cheap at garage sales etc. The handle shown here isn't as long as I would like for some tasks, but it is longer than usual.
A khukuri like this is a very good chopper and a stabby blade.... if you can get used to the handle not being parallel to the blade (something which I found to be difficult to adapt to). I don't own a khukuri currently. I still like them, but they were always a bit difficult to carry. I'm sure there are many folks who would pick a khukuri as their 'one tool'.
My golok is the knife at the top of the picture with the string around the handle. This was great on the trap line for chopping work and clubbing the possums that I caught. But it didn't fulfil my need to have a pointy blade. Plus it is fairly heavy and cumbersome. I keep it under the seat of my vehicle now. It is a handy chopping, levering, and hammering tool.
We generally have the luxury of choosing from a variety of tools. Our ancestors had to improvise with cruder implements like this small hand-axe that was found at a site that is well known as a place where whales have become beached over the years.
So... in conclusion.... circumstances differ. Right now if I had to pick one tool for general purpose help in the wilderness it would be a pointy knife of a reasonable size.