Tackles, and in particular left tackles, tend to be the elite positions on the offensive line. The position requires linemen to generally have the best size (height, arm reach) and athletic ability (agility, technique) in order to deal with one on one pass rushers. Left tackle in particular is crucial as this lineman protects the blindside of a right-handed QB.
Guards tend to be smaller than tackles, though at the pro level this is largely because these players simply did not have the measurables to project as a tackle. Unlike tackles, guards will be more likely to work in double-team assignments, such as with the center against a nose tackle. Guards are also asked to 'pull' in running and rollout plays which requires the linemen to turn and move quickly down the line of scrimmage in order to deliver a crucial block to create or seal a running lane.
Centers tend to be as small as guards, though they're best thought of as specialists. Where as tackles have a physical skillset that distinguishes them from guards, centers have a tactical responsibility that makes them unique. They call out blocking assignments at the line of scrimmage and are responsible for the snap. It's a unique skillset that makes it hard to simply slot any lineman at the position. Centers usually take longer to develop and adjust to the pro game as they adapt to the many confusing defensive looks and blitzes used at the higher level.
In the NFL, left tackles are generally the highest earning lineman. They're considered franchise players as even an elite QB cannot pass effectively without an above average tackle holding down elite pass rushers. Centers can make more than guards, but the pay difference in recent years has really just come down to the player's fit with the team. A center for an elite passing team is likely to make as much as a guard for a strong inside running team.
