Welcome to the forum rlfmom and I take it you or a loved one must be affiliated with the military. Thank you for serving our great country!
Choosing between credit card miles vs points depends on the card because the terms are used interchangeably. A true "miles" card will be one associated with an airline that gives miles on spending. Those miles can be converted to flights at given intervals, irrelevant of the ticket's cost - i.e. off peak roundtrip flight for 25,000 or 37,500 miles.
There are general travel cards not affiliated with specific airlines that advertise miles but it would be easier to think of them as points or cash back since typically 1 mile = 1 cent that can be applied to a travel purchase of your choice. An example of this would be the Discover Escape
with its 2 miles per dollar spent, which equals 2% rewards.
For spending of $4,000 monthly with a significant portion on gas and groceries I would strongly recommend the Blue Cash. Credit Card Forum advertises the card and has a detailed American Express Blue review
which should be helpful.
For comparison of travel cards, here is a sponsored ranking of the top 10 travel rewards credit cards
All the best,