IMO, there are pro's and cons to both.Ran a few numbers....
Took a shot at yearly hours on a ZTR being 500 (nice even number most of us have no problem achieving in a good season)
To keep things simple on consumption:
Gas I rounded to 2 gal/hr and used $3.60/gal
Diesel I rounded to 1 gal/hr and used $4.30/gal
I used GasBuddy to get these prices.
GAS = 500 x 2 = 1000gal x $3.60/gal = $3600 annual fuel cost
DIESEL = 500 x 1 = 500gal x $4.30/gal = $2150 annual fuel cost
So, first year, the DIESEL would save you $1450 in fuel.
Now you have to add in the initial upfront cost that a diesel has. This is where numbers will be all over the place.
I was figuring a 1L Big Block gas 72" ZTR versus a same manufacturer 3 cyl Diesel.
Is it safe to say you can get a gas ZTR for $10K ?
Is it safe to say you can get a diesel ZTR for $14k ?
Your looking at close to 3 years to break even.
Today's 1L Big Block gas engines are VERY powerful. Often times MORE powerful than most manufacturers Diesel offerings.
Then you have the weight. A couple hundred pounds at least.
Food for thought and discussion.