The SQL Developer position is heads above the other position for career development and growth. Just a ballpark guess here, but my guess is you'll learn more in a year with the SQL Developer position than you would in 5+ with the BI Specialist position. The SQL Developer position is going to expose you to more of the "meat and potatoes" of this world and you'll get the bonus of working with a team and learning from them and bouncing ideas off of each other. Sorry, but your MIS director doesn't know what he's talking about unless there is some information that you haven't given us about the two positions. No brainer.