Enclosure size and flow are the practical limits. A large rainfall head needs the space and water flow to feel right, whereas a handheld suits almost any layout. Choosing by routine rather than by looks alone tends to give the most satisfying result. To compare shower heads across the range, see https://swfconsultinggroup.com/question/because-the-finish-is-textured-rather-than-reflective-the-small-marks-of-everyday-use-are-less-obvious-than-on-polished-chrome-which-keeps-fittings-looking-settled-for-longer-for-a-bathroom-that-ge/.