If you can handle the risk of ending up with a compact, then go for it - reserve the cheapest thing possible and ask for an upgrade. Sometimes reserving car with XM/Neverlost helps. also, reserve on Friday Morning or even a Thursday when most eco cars (business reservations) are still gone and fun cars (tourists arriving during weekend) still at the lot. Be nice to manager, if he/she is a car guy you may be in luck.