Most exterior paint doesn't fail because of the brand on the can. It fails because it went on over dirt, chalky old paint, or open seams. In North Texas, where summer surfaces get hot enough to burn your hand, any weak spot in the prep shows up within a couple of seasons.
A lasting exterior job starts with washing the siding and trim, scraping off anything loose, and caulking the gaps where water gets in. Bare wood and metal need a spot primer, because paint won't bond well to raw surfaces on its own.
Then comes the finish. Exterior-grade paint made to handle heat and UV keeps its color longer and stays flexible as siding expands and contracts between 100-degree afternoons and cool nights.
When you compare estimates, ask each painter exactly what prep is included. If the answer is vague, the price is probably low because the prep isn't there.