Either one will tow your trailer and haul the kids in comfort and style. I drag a similar trailer with my 2016 5.3/ 3.42 gear Silverado half ton and it does well at low altitude.
If I had my druthers, I'd want the 6.2 GM or Eco Boost for heavy towing like that, but I'm sure you're looking for a balance between daily driver and tow pig.
Basically 5.3 = 5.0 Ford
6.2 = Eco boost
They both come with 10 speeds now, correct?
I think it's a toss up save for the extra snort of the Eco boost being readily available in the Expe.
They both look sharp. Looks wise, the new Expes look like a Tahoe anyway now.