Having started with ATR72s, I have moved into jets with 737-200s, primarily due to low lease costs (and lack of 733s available for lease) in order to operate longer routes. I make sure that any I lease have had D-Checks recently, and ideally at least 8 months to C-Check, and under 20yo on leasing. I reseat to 10C/102Y, as this suits my routes which have some C seat demand.
I am acquiring 733s as they appear but lease costs are a lot higher, which in the current time more than offsets the lower fuel use of the newer aircraft. At this stage, I cannot afford to tie up $5m+ in lease fees for 7 months for a new a/c.