What are the pros/cons for re-enlisting versus extending?

If there is a re-enlistment bonus you can get some money. Extending is only a one year commitment. If your rate is being downsized you might want to re-enlist so you can serve longer if you want to.

re-enlisting often comes with benefits and options as it is a brand new contract between you and the branch whereas extension is simply extending the term of current contract. Additionally, the branches usually have certain terms for extension and they can only be used "x" amount of times for "x" reason. I extended my enlisted contract 1yr while I was pending a direct commission, had I re-enlisted, my chain may not have signed my conditional release to accept a commission.

Re-enlisting bonus might be better and choices if Duty station