We almost always rent using Enterprise (including our upcoming trip in August) for both personal and business. So far, I've never had a problem with them, and while do push the upgrades/insurance (as do a lot of them), I've never found that they are pushy if you decline either (at least I don't think so). While others may disagree, I've always found the cars to be very clean, in good mechanical and physical condition and their agents to be quite knowledgeable. On our last trip to WDW, we rented through MCO and, while I can't be 100% sure, I believe they upgraded us to a larger vehicle size at no cost.
I would put in a reservation if you haven't yet, as you lock in that rate, but can always cancel/modify if the rate drops or you find a lower rate with another company. Even if you don't join their Enterprise Plus program, sign up for emails. I got a 15% off email this morning from them that lowered our price down about $40. Its not a huge discount, but I'll take it.