I would suggest you send it to me.
I have a 19, 26, & 20. Each has their merits.
I have a few questions to help you decide.
What is your intended purpose of the gun? Carry, range, competition, etc.
Do you concentrate on a select few calibers, like me, or do you want a big diversity?
Do you already own a Glock and want a compatible big or little brother for it?
Is it for urban or rural environments?
All of mine are gen 3; so, I can't make a suggestion between those two. Gen 4's are usually more expensive, though.
If it were me, I'd get another 19 in a heartbeat. I think it's the best overall frame size and offers the most versatility. The 26 is my standard carry gun and is a little lighter and more concealable. The 20SF is my woods gun.
Hope this helps.