Need a little more info before advising.
Is your next investment a real estate investment and is it happening soon? For sure? Or only maybe? What kind of purchase price are you talking? If buying again soon, I'd sock away but keep liquid 20% of ballpark purchase price for a downpayment, or in cash if you plan to purchase very soon. If no new purchases planned in the next ~2 years, see below.
Are any of your mortgages higher interest? (more than say, 5%) You'd want to pay those higher interest loans down, but may as well keep the low interest loans.