To distinguish the two, which we don't often see in live action, Brandon Routh may come close to that where he had really floppy hair as Clark but tidy hair as Supes.
shareIt kind of comes down to which is the dominant identity, Clark, or Superman. The dominant identity will get the better looking hairstyle. Pre-Crisis on Infinite Earths, the comic book version of Superman had Superman as the dominant identity, and the Christopher Reeve movies took their inspiration from pre-Crisis Superman. Superman is who he really is, and Clark is a disguise to let him fit in and have a semi-normal life, and this is why he doesn't mind Clark being a buffoon, a total dork, and a laughingstock that Lois will never even really respect, let along feel attracted to.
Lois and Clark took inspiration from the post-Crisis, 1986 reboot, which made Clark the dominant identity, and Superman was just a persona Clark adopted to allow him to use his power to help people without giving himself away to the world and losing any opportunity to fit in and have something like normal life. And, accordingly, throughout the series, Lois gradually gets over her infatuation with Superman, and comes to realize that Clark is the man she truly loves and wants to be with.
Clark is who Kal-El really is when you get right down to it, that's why he (really the series' producers) chose to give Clark the more physically attractive style.