A mat is the thing standing between whatever is happening outside your door and the floor you just cleaned. Rain, mud, salt, dropped leaves, whatever the dog rolled in, it is supposed to catch it before it gets any further into the house. That is the whole job, and a surprising number of mats quietly fail at it after a few months.
Getting the size right matters more than people think when they're standing in a shop holding one. Measure the actual space in front of your door, not the door itself, and account for the swing of the door so it doesn't catch and bunch up the mat every time someone comes through. Outside, go bigger than feels necessary, you want enough surface area for two full strides so both feet make contact before anyone reaches your hallway floor. Inside, a smaller mat right against the threshold does more work than people expect, since it catches what the outside one missed. If you've got nothing yet, start with a solid outdoor mat at the main entrance, that's the one doing the heavy lifting, and add the indoor one once you've got a sense of how much mess is actually coming through. What separates a decent mat from a disappointing one usually comes down to the backing and the fiber. A rubber or vinyl backing that stays flat and doesn't curl at the corners after a rained on week beats a flimsy one every time, and natural fibers like coir hold grit without looking matted down within a month, though they're rougher on bare feet than something like polypropylene, which dries faster and doesn't mind getting hosed off. Cheap mats tend to shed, fray at the edges, or go flat and shiny where feet land most, and once that happens they stop scraping anything off your shoes and just sit there looking tired. The day it arrives, check the edges are properly bound and not just cut, run a hand across the surface for any loose fibers, and make sure it actually lies flat without curling, since a mat that won't sit still on the floor is a mat you'll trip on eventually, and a bad fall right at your own front door is not the way you want a Tuesday to go.
I'd put the first one down at the main entrance, the door everyone actually uses, not the pretty front one nobody touches. That's where the real damage happens, and that's where a good mat earns the ten minutes it takes to pick the right one.