What would the best motor oil to replace in my 2003 aztex

At this point, I would recommend getting a high mileage oil. If I recall correctly, it should use 5w30. It should be written on the oil cap as well as your owner's manual.

I personally have always used Valvoline, but I am not allowed to recommend brands.

It should be. I recommend checking the owner's manual. Usually, they provide different options based on outside temps. I don't know where you live.

The manufacturers have started using a lighter grade of oil so it circulates quicker to all locations. They have tightened up tolerances in the engine. As a result, to get quicker oil pressure, they went to the lighter oil.

Check the owner's manual to confirm recommendations / temps. Please understand, I can't guarantee anything, but 10W30 shouldn't hurt anything unless you are in an extremely cold environment. I'm sure if you need to, the parts store will exchange the oil you already got, so don't worry. One thing I will recommend is to get a brand name oil filter.