I've rented from both Omega and Apex in CHC.
Have only tried them once, but I will never go back to Apex - they tried insisting that a car was perfectly fine when I could tell within 2 minutes of getting behind the wheel that the front discs were warped and it had been curbed at some point.
Omega is my first choice for rentals in CHC. Friendly, reasonable range of cars and prices, and easy to deal with, no upselling BS.