I would definitely go with the Note 3 and Gear but you know these questions are always subjective. I have nothing against the S5 except it doesn't have an S-Pen. Well depending which carrier you're on it may also only come with 16GB internal storage, which I wouldn't like either, but that may not be true with yours.
Since you've used a Note 2 before and you already have the S5 you should have a pretty good idea of what you'd like better. Throwing in the Gear watch, assuming you'd use it, it seems like a no brainer to me. But if you don't care about the S-Pen and you like the smaller size and slightly newer hardware of the S5, I doubt you'd be unhappy with it for 5 months.
The only thing I would prefer about the S5 myself is the water-proofing. That alone is not enough to get me to choose it over the Note 3.
Just editing to add that this was based solely on a phone comparison, not on whether or not it's wise to swap phones with someone else. You didn't state the circumstances of the swap. If you're taking about swapping with someone online, I'd run from that and hold on to your S5. If you're talking about swapping with a good trustworthy friend or relative, go for it.