For Lawn care I charge by the thousand square feet, by the acre, and often by the hour since I know how much I can "spend" in an hour and what I expect to generate and it is comparable to a straight up square footage price.
For Tree care I have several standard levels of pricing for residentials, in other words your basic 75-125-175-225 dollar apps. For commercial tree care prices are basically an hourly rate. Pricing tree care is a lot more challenging than lawn care.
For seeding and aeration It's a combination of an hourly rate and square footage.
Pricing a service consists of two things and two things only.
What it costs you and what you expect to make. Period. It doesn't matter how you do it.
Oh. I forgot to mention I charge a premium for anyone on a dirt road. Armor All is expensive and washing my rig takes a good hour and I don't do dirt roads on rainy days.