Only ask for T5 if you're willing to put in the work - it lacks a decent equipment list, instead giving you construction routines for making your own lists. Same with the vehicles and ships, tho' the specifications for the standard ships are in shorthand form.
If I had one wish that I could wish for this Holiday Season, it would be that WoTC would announce Greyhawk and all the gamers of the world would join hands and sing in the spirit of harmony and peace.
If I had two wishes that I could wish for this Holiday Season, the first would be that they would announce Greyhawk and all the gamers of the world would join hands and sing in the spirit of harmony and peace. And the second would be that WoTC would give other people stuff they want, too.
You know, if I had three wishes I could make for this Holiday Season, the first, of course, would be that they would announce Greyhawk and all the gamers of the world would join hands and sing, the second would be for people getting stuff they like, and the third would be for me receiving 30 million dollars every month. Preferably tax-free.
And if I had four wishes that I could make this for this Holiday Season, the first would be the crap about Greyhawk and the gamers getting along and stuff and singing, the second would be other people getting nice stuff or whatever, the third would be for the money, and the fourth would be for encompassing power over every living being in the entire universe.
Wait a minute, maybe the all-encompassing power should be the first wish, because it could all go boom tomorrow, then what do you got, y'know? No, no, Greyhawk and all those gamers singing and getting along ... that would be great, that would be nice. But wait a minute, who am I kidding? They're not going to be able to get all the gamers together. I mean, the logistics of the thing is impossible, more trouble than it's worth! Not to mention ... have you seen people lately? Have you even read facebook or twitter? So -- we reorganize! Here we go. First, the power. We go with that. Second, the money. And then give other people what they want ... NO, wait, we give ME what I WANT. Which is Greyhawk. And other people singing and stuff. Oh wait, oh jeez, I forgot about revenge against my enemies! Okay, I need revenge against all my enemies, they should die like pigs in hell! That would be my fourth wish. Actually, maybe that's my first wish. Mostly because of social media. But let's assume I have four wishes.
And, of course, my fifth wish would be for other games to get stuff they want. As long as it's Greyhawk.
I've been running campaigns in the World of Midgard since 2012 and I'll just say those 2 books you listed are very good. There's about 800 pages of Midgard, gaming goodness between them. What I like best about the WoM book, is that about 90% of it is system agnostic. So if you don't want to run your campaign with the D&D 5e rules (my WoM has PF1e content too, but I think that's omitted in the latest printing), there's lots of other possibilites, as there's a Midgard Bestiary for more than a handful of other systems. I've run Midgard adventures with True20, Fantasy Age and D&D 5e. And I'm currently prepping to run a campaign with PF1e.
I'm only slightly familiar with the Traveler 5 CRB, which I browsed thru at length at a LGS about 3 years ago when I was looking to take a plunge into the system. So can't really weigh one choice against the other.