seniority means nothing unless you are at the airline you want to be at for good. seniority isn't marketable like experience is. you can build time faster as a cfi than you can at a regional since as a cfi you won't spend time in long training or on reserve. you won't regret being one where as you may regret jumping to a bad regional in order to get on with a better one. a cfi who builds time the "old fashioned" way has in my opinion also been more respected by other pilots.