Who is your best dweller to send out and explore? I'd have to say mine would be Jericho. He's currently Level 48, a Legendary dweller I got from a Lunch box, and is equipped with a Heavy Leather Armor(Legendary) and an Infiltrator Assault Rifle(Legendary). I've sent him out constantly and he's always come back with tons of stuff. He's my main for wasteland exploring and scavenging.

Mine are all the level 50s with full max stats outfitte with the best weapons (like minigun or the much more common plasma rifle) and that dog that gives 2x return speed.

As you might notice, the characteristics of individuals don't matter, in fact they don't exist.

I have a guy that went out for like two weeks, so it's still another 48 hours before he returns to the vault. He only stopped because he ran out of room to collect items. He was level 1 when he started, it probably took him like 12 hours to get to 50.

I don't send out lvl 50s since they don't gain levels, I've since been training newborns and visitors in the various rooms before they head off. Once they come back they're forever relegated to making water or meds.

I'm also older player. I use wasteland to level up. Set all stats at max and then sent dweller to level up.

About half the total dwellers in my vault right now were all raised from lv 1 children to max stat, then equipped with heavy wasteland gear and sent to the wasteland to level up to 50. By level 50 they have 644 HP (IIRC) which is the max possible.

All of them can completely fill their inventories before returning to the vault with medpacks to spare, when equipped with legendary armor and weapons, and +health or damage resistance pets. Using FSSE to purge their common items before they fill up, the longest expedition I've gotten out of them was roughly 11 days if sent out already at lv 50, or about 13 days if sent out at level 1 (since every time they level up, they fully heal, this extends how long they can stay out in the wasteland before they start using medpacks)

My ultimate record was around 16 days using the exploit from the previous update, where you could level dwellers to lv 100 using muttface, however to make them not crash the game, I had to use FSSE to edit their level back down to 50 before sending them out. Now with the latest update, all of their extra HP from leveling like this has gone away and they're like any other dwellers, so I doubt anyone will exceed 16 days again in the future (unless they're using the particular exploit where they just don't open the game for 16+ days after sending the dweller out, so you get a dweller that has been out for a very long time but only encountered ~ 5 days of actual events)