I can't make a recommendation on the best brand to buy since I've not tried them all, but I have the Invisible Fence. I bought the unit about 15 years ago and it has been working flawlessly even since. As for the wire, I bought a spool at Home Depot. I purchased the type wire suggested by Invisible Fence. So I don't know if different fence systems require different size wire. But it surely is much cheaper buying it by the spool from a building supply source.
I didn't bury my wire. For ease of installation, maintenance, and relocation I have it on stick-in-the-ground plastic electric fence posts. Besides, my
land is extremely rocky and it would be a Herculean challenge to bury it.
I don't think your old electric fence wire would work. I'm just guessing on that. All the "radio" invisible fences seem to be using copper strand wire.
The are a couple of reasons for failure with these fences......
....they don't keep trouble makers out. Stray dogs can freely enter your property to attack your dog.
.....an excited dog can bolt right through it while chasing a cat,
deer, whatever.
.....they don't prevent someone from stealing your dog. I'm specifically directing this toward over zealous SPCA/Humane Society dog catchers. I caught one trespassing on my farm and trying to take one of my farm dogs, claiming it was an at-large stray. I had to call in the police to get my dog away from her (after I blocked her truck with my own vehicle so that she couldn't drive away with it). Boy I was tempted to file attempted theft charges that day. She sure wasn't happy giving me the dog back.
.....and the ultimate failure -- the dog wasn't successfully conditioned to respect the fence.
The dog needs to be well conditioned about the fence and warning beeps. The idea is to make zero mistakes. The dog needs to believe that it never can get through the fence, that it will always bite him if he tries. This type of canine thinking takes advantage of the dog's innate nature to submit to the more dominant dog. He must believe that he can never beat the fence. Over the years I've conditioned over a dozen dogs to the fence. Some were harder to train than others, but all managed to catch on. But alas not every owner is successful. My parents attempted to train their one dog and failed miserably. Their dog learned that it could take the jolt and run through the fence whenever it wanted.