Real consoles. Since emulators have become a pain in the ass to configure all the settings and not all of them work properly, I can't stand them anymore. The only one I use it is VBA (and, once in a while, the snes9x) because they are simple and work flawless. But all the PS1, N64 and DS I've tried never worked smoothly, always had some problem ;_;
DS emulators were my worst experience. "You can't save on this one", "it only plays at 80% of the speed", "it randomly freezes", "you need to use gameshark to continue" ... nah. I rather not play than to play and get mad when I can't progress anymore.
I'd say backward compatibility should be hardware instead of software, to avoid these random problems.