I think it really depends what you want to use your pen for.
If you want it just for signatures, I would get a pen that has a broad nib.
If you are using it to write a lot, you will have to experiment.
Depending on your paper, you will have to change the nib sizes.

Fountain Pens 

Satosora

I think it really depends what you want to use your pen for. 
If you want it just for signatures, I would get a pen that has a broad nib. 
If you are using it to write a lot, you will have to experiment. 
Depending on your paper, you will have to change the nib sizes. 