Subdomain vs. Subdirectory in Multisite Install

Im finally getting ready to set up my multisite install to use many of your various tools.
What is your recommendation regarding setting it up as a Subdomain vs. as a Subdirectory?
The biggest difference I can see is that I like the visual appeal of sub domains better in the address bar, but it looks like I could save substantial money by not having to get a wildcard SSL certificate if I go with Subdirectory. Just want to confirm that I'm correct about the way I'm viewing it and see if there are other considerations I need to be taking into account.