For those who fly out and into Centennial airport in Colorado, which air service is preferable for general aviation (my RV7a), and is their a charge for overnight parking. I will buying the expensive gas.
I've been into APA a couple times - and have always used TacAir. I get their SServe gas - which is generally cheaper. They've told me that they'll let you park for free ... but will charge you $10/night (if I remember correctly) to tied down (no free nights for fillups). It's just too windy to leave it parked - so I pay the tiedown.
I just got back from Denver and used FTG instead ($5/night) because I had a longer stay. The fuel price at FTG was w/in a penny of APA.
I've been to APA twice and used TacAir both times. I posted a question similar to yours on the AOPA board before my first visit and TacAir was the one most recommended. Tiedowns are $10 per night (as of mid July at least) and SS fuel on the north end was very reasonably priced. Very nice facility and friendly staff. I would definitely use them again.