We've had good results with Tape Technologies and lately Oracal's banner tapes. I used to hate Oracal's, but it seems like they reformulated the adhesive or something because it sticks a lot better than it used to.
Make sure you're cleaning the backside of the banner with alcohol before applying, and be sure you're squeegeeing/rolling the tape HARD. We've noticed some brands of banner like tape better than others, some have a lot of coarse texture on the back that the tape just doesn't stick to all that well.
IMO with the right combination of banner material and tape, tape hems can be as strong, or stronger than sewn hems. But they're expensive if you start adding up how much tape you use. We never really paid attention to it until I did an inventory audit one day and realized we were using upwards of $700 a month of banner tape. You can get a really good industrial sewing machine for about $2000-$3000, so that purchase was a no brainer. If you're using a lot of tape, you'll see an ROI on the machine purchase in a few months, and beyond that, it's almost free to hem banners then because thread costs just a couple pennies at most to hem a banner.
