To be pedantic, although Farseer and Martuuk offer the same G5 FSD mod's, they offer other, different, stuff too.
Auntie Felicity is probably the best "get you started" engineer.
She offers her FSD mod's and lower-level mod's for thrusters, power plants, sensors and other stuff too.
Martuuk offers some lower-tier stuff as well but really the only thing that's useful is her mod's for your Shield.
When it comes to pinning blueprints, the way I looked at it was that if I'd pinned an FSD mod' from Martuuk, none of Farseers other "get you started" mod's would have been useful.
That being the case, I pinned the long-range FSD mod' from Farseer and then I pinned a Shield mod' from Martuuk - cos the ability to apply a G3 Shield mod' is, at least, fairly useful.