Big picture… if you are platform agnostic, we have more templates and workflows available in Sheets. The upside of Excel is mostly that the add-in is more responsive.
Sheets has two add-ons— Tiller Money Solutions (for supported templates and your feeds) and Tiller Community Solutions (for community supported and beta workflows and templates)
Or did you mean templates, @sblagoue? The Excel templates are limited to what is in the add-in and what you can find in community Show & Tell. On the Sheets side, many templates are listed in the Tiller Community Solutions add-on and there are MANY more in the in community Show & Tell.