FWIW, if you use Gmail for email, calendar and contacts, set up 2 accounts on the iPad. Use Exchange and connect to Gmail for Calendar and Contacts and set up a second non-Exchange for Gmail using IMAP.
This will keep your calendar, contacts and email synced up the "best" from what I have seen. If you use Exchange for Gmail email, it can hiccup once in a while for no reason at all.
Even though you use 2 accounts, everything works seamlessly.