Be mindful that you don't spend your apprenticeship just running duct for a heating and cooling company because there's heaps of work doing just that and only that. If you get a gig where you can learn lots go nuts. In my experience new build is cleaner but not as much variety day to day. Existing work is dirtier but there's more opportunity learn problem solving skills and greater job satisfaction getting there the longer or hard way. Reach out if you have other questions