Don't know why, I'm sure it's one of the standard fonts shipped with access, the only font I've seen recommended is the one that causes NoLicence errors strangely Hattenschweiler
I prefer sans serif fonts. Ariel is the default font and the one I use for most labels and data fields. Ariel is also safe since it is always installed with windows. If you use a non-standard font and don't install it on all the computers that will be using your app, Windows will substutite some other font which may look terrible so be careful.