For Superman,
If you want to a birth to death type of experience, I recommend the alternate worlds Red Son. As for reboots, Secret Origins and Man of Steel have been mentioned already, but I might've missed Birthright. This reboot had some Smallville influences, which might be appealing to you or turn you completely off. I really liked the artwork.
For Batman,
For arcs, I really liked Knightfall Parts 1 and 2. Knightfall Part 3 was okay, the artwork wasn't as good. I also recommend Year One and Dark Knight Returns. The Killing Joke and Death in the Family are both monumental works that show how Batman deals with peril for those he cares for, if not being imperiled himself necessarily. Last year's Batman RIP works better as a TPB than stand alone issues. The artwork for RIP was good, but the story had some loopy turns so I recommend holding off on that one for a bit, if you were inclined to read it at all.
There's also the current running Superman/Batman comics, but I can't vouch for their consistency or quality. I've only read two of the TPBs, the one with Supergirl and Public Enemies, which was recently adapted to an animated movie.
If you want to a birth to death type of experience, I recommend the alternate worlds Red Son. As for reboots, Secret Origins and Man of Steel have been mentioned already, but I might've missed Birthright. This reboot had some Smallville influences, which might be appealing to you or turn you completely off. I really liked the artwork.
For Batman,
For arcs, I really liked Knightfall Parts 1 and 2. Knightfall Part 3 was okay, the artwork wasn't as good. I also recommend Year One and Dark Knight Returns. The Killing Joke and Death in the Family are both monumental works that show how Batman deals with peril for those he cares for, if not being imperiled himself necessarily. Last year's Batman RIP works better as a TPB than stand alone issues. The artwork for RIP was good, but the story had some loopy turns so I recommend holding off on that one for a bit, if you were inclined to read it at all.
There's also the current running Superman/Batman comics, but I can't vouch for their consistency or quality. I've only read two of the TPBs, the one with Supergirl and Public Enemies, which was recently adapted to an animated movie.