I use Tuff Tape from Fellers it's the first one at the top of the page in there catalog.
I don't like Oracal I have had the same problem as insignia.
I've been using Oracal for lo these many years and have never, ever, had a problem with it.
Perhaps your technique is inadequate. For any flavor of tape you should do the following...
When you run the tape on the banner and before you pull off the backing, you should run a squeegee along the tape to force it down on the banner material. You should see the weave of the banner material in the tape backing.
You should run a narrow breyer roller along as you fold the banner material to make the hem. Run the fold and the roller right behind it with a short back and forth motion. Don't fold the entire edge and then try to force it down.
Do it this way and you'll never have a hem come untrained no matter what brand of tape you use. Which, since it's a fungible commodity, should be the cheapest you can get.
The only tape I every tried that I absolutely refused to use was a couple of rolls of brand X tape that apparently was parted from the main roll with a chainsaw or something. The edges of the rolls were so rough that it was impossible to peel the backing without it tearing and leaving chunks of itself on the tape.
