If you buy saga you know you are going to get some of the best quality
And saga is much waterproof with the new 3L jackets and saga is just s shell jacket but still very varm.
First Drop on the other hand I'm not sure about, but last year the where shitty quality. But it seems that Lesh have stepped it up big time to get us the best. First Drop is insulated jacket and not just a shell.
So you should think about it and buy the jacket you like the most.
Anyway you will be satisfied.
Btw: I had saga last year, but bought First Drop this year because I think the design is way cooler and I love the zip of sleves.