First, you don’t tell us if you are looking for a walk behind or ride on mower, as you look for totally different things. I’m going to assume that you mean walk behind and us it for my answer.
1. What type of landscape and size do you have? If it is less than 1/4 acre and flat, you don’t need a self propelled unit. If larger or has some slopes I would definitely recommend a self propelled unit.
2. Are you bagging, mulching, side discharging or all of these depending on season?
3. Which major brand names do you have in your area? I always recommend going with a major brand name, Toro, Ariens, Simplicity, Honda, Snapper, etc. I will never recommend a unit built by MTD, which are sold by the Big Box stores.
4. Which dealers in your area sell the major brands? Are there dealerships in your area which have a bad reputation on service? Have you been comfortable with any of the dealerships in your area? I always recommend buying from a dealership whenever possible.
5. Are you going to be the only user of the unit? If not get the other persons input. You make the final decision, but you want them happy using the unit or you’ll loose your help.
6. Ask your friends and neighbors, who have the major brands, what they like or dislike about their units.
7. I know that price is always a consideration, but most times paying more up front is better. I would look for things like cast deck, metal drive wheels, engine type and size, comfortable handle and drive system, etc.
Finally being a Toro guy since the 80’s I’ve got to say this in closing. I have recommended the Toro Super Recycler mowers for the last 40 years. Hope this helps, if you are looking at ride on units, I’ll post those rules later.