There are a lot of opinions about this and depending on the ryu you'll hear different informed opinions. As a guy who gets to see damaged swords a lot... Edge to edge, edge to back, straight on, deflected... they all damage both blades. The "hollywood" conception with guys whacking each other's swords left and right would result in one thing only -- ginsu knives for both.
Which is better? Well made blades generally won't snap due to edge to edge or edge to back strikes. It simply takes too much force to do that and consider that both swordsmen are holding the swords with their wrists. Notice I said well made as a caveat.
A while back Tony Alvarez and I (along with a group of other swordsmen, MA's, polishers and smiths) tested a theory about blocking a sword with a jo strike while we were taking a break when we were being interviewed for a short film. He cut through my jo but it took one hell of a whack by me to get the speed up while he swung full speed (what the hell were we thinking?). Cut it like it wasn't there. The first time we just kinda let the jo and sword meet and the sword took zero edge damage but a huge chunk came out of the jo. Wood is much softer than a martensitic edge so with proper hasuji by the swordsman the sword generally won't take damage.
But whack even the soft back of another sword and the edge will get a bit of damage. I've seen it. We've done it in testing swords.
Folk argue over what would most likely cause a break. During that same weekend when we were being interviewed we took a couple blades out back and rigged up a test. We went edge to back using a Clark L6 bainite as the cutter and a well known "beater" brand 5160 sword as the unlucky recipient. The 5160 blade was bolted to a thick post that had been sunk into underground concrete slab. The strikes to the mune left serious cuts to the 5160 steel (an "idiot proof" heat treat steel that is very tough). But nothing to break it. The L6 took minor damage to the edge, but it was slightly damaged. Nothing fatal and nothing a polisher couldn't remove, but there was a small hakobori.
We then flipped the 5160 blade over and tried edge to edge. The first strike by "Big Tony" was so powerful it knocked the bolt clean out and the blade fell. Serious edge damage to the 5160 blade. Repairable in a sense, but it would be a serious repair. The edge damage to the L6 was considerably less even though the 5160 blade was thicker. But it did take a bit of damage. On the next strike edge to edge the 5160 blade snapped clean in half. But the odd thing was that the blade didn't snap at the point of impact. The cut against the edge cause one of the cuts to the back nearer the tip to propogate towards the edge and the blade snapped that way. And that was the "free floating" end of the sword. Surprised us all including the two swordsmiths who were there.
So the question is whether the ha strike or the mune strike "broke" the blade. The blade survived both in a sense. But one ha strike cause the prior mune strike to propogate the blade failed.
So, does this answer any of the questions?
I was there and I still don't know the answer. I've repaired a lot of blades that have taken damage over the years. Mostly from guys hitting pegs and stands at off angles. Also, remember that mune cuts on antiques are considered by some to be "valuable" in that they show the blade saw use. I wouldn't even try to say which is better.
And I must also add that with each style I'm familiar with (a small handful and more from discussions with my customers when they need repairs), none of them advocate ever trying to take a strike head on. There are lots of deflections, redirections, etc. taught. When it comes down to the "oh-God" moment and you realize you're going to do a hard block, well, I've heard very high ranking people say the ha is best and very high ranking people say the mune is best. One sensei I met had the best answer, I think. He said block with whatever the hell is closest and pray to survive...