I would go with a quality ro. With city it is a mixed bag and you never really know what will be in there. Whereas with ro (especially ro/di) you can always add in only the minerals you want, whether that be with a good quality salt or with just the minerals themselves. (kent products, etc.)
IMHO I would recommend for anyone new to the hobby; going with a high quality salt and the ro or ro/di and worrying about possible additives later when more experienced. If the tank doesn't have hard coral or sps chances are you might not have to add anything.
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