That's a difficult one to answer Tim, as with all my CS ac the question is, 'What shall I fly today?' and that depends on where I want to fly as I like to keep each airline in its home skies.

For that reason I prefer the 727 as with more liveries it gives me more geographical options. (I've yet to learn how to get repaints). For example today I flew a Northwest 727 from KORD to KMSP just to enjoy some filthy weather, snow at KMSP  :)

With only five liveries in the base 737 my regions are limited, having said that, I fly mostly around Europe and N America and short to medium hops due to time constraints.

I suppose I fly the 727 more because I've flown on more of them than the 737 and I prefer the look of it, it looks like it means business, it's grubbier than the 737, the cockpit is well worn. My only complaint is the foot warmer does work.

In terms of quality of product there's nothing in it really, along with their 707, 777 and L1011, they all compare.