Lots of good informations here!
I'm not an expert by any means, but I'll share my opinion based on my personal experience. I dedicated quite some time developing my foot technique and I thought about this exact subject so many times.
The two techniques are different from each other but somehow can look similar, so it's not easy to see the difference sometimes. Every person develops some kind of a personal way to execute them based mainly on body genetics and comfort. Some are more prone specifically to one of them, some others find some kind of an hybrid between the two or do something completely different from both. There's so much going on when it comes to foot technique, it's fascinating.
I practiced both and theoretically I prefer heel-toe just because I don't like the idea of moving my right foot back and forth. Pratically, I developed my personal way to execute double strokes which I'm not sure how to call it, but I guess it's a mix of the two which works with ANY pedal.
If you try to execute the slide technique doing a little tap with your toe and then letting your whole leg fall down (instead of sliding the toe forward), you'll see your foot going slightly forward anyway, it's physics. So it can look like a slide but it's more like an inverted heel-toe ("toe-heel"?). I also want to point out that the "heel" strike doesn't necessarely need to be executed with the heel, you can still do that without touching the pedal. So....
Is toe-heel still heel-toe?
Is toe-heel a variation of the slide?
My suggestion would be to practice both heel-toe and "toe-heel" (if it's even exists) and play with accents, because imho it's all about the accents and the proper technique to highlight them.
Slide is also very effective, very fast and more natural to execute (imho), but like I said I prefer to rely on foot stability and move it as less as possible.
Practice all of them and find your way.