I didn't have issues when choosing because where I live you need proper education to do nails (beautician). There are plenty of courses with licenses and National Vocational Qualifications, none of which are accepted when you're trying to open a salon (I don't know how things are if you're trying to work in someone else's salon but from what I know they prefer if you're a certified beautician). In my school I'm learning to do facials/facial care, body care, manicures, pedicures, makeup and massage.
With that said if I had the option to only learn to do nails, I probably would, provided I would be taught everything properly, like I am in school (skin structure, nail structure, sanitation, preparation of the technician, working space, client, contraindications, analysis of skin and nails,...) as well as variety of services, such as natural manicure, gels, acrylics,...
However, I think that learning how to do multiple things and getting multiple practical experiences is good, even if you're not going to offer absolutely all of the services in your own salon, because should something not work out, you will have the basic knowledge and will be able to offer other services. It's also easier to upgrade the knowledge you have in the future if you ever want to specialize in something else.
I know things are different in practically every country and money might play a big role in choosing which courses/classes/schools people pick, I do want to say that it's better to invest in quality training if you can, as money spent on knowledge is money well spent. It might also be cheaper in the long run, rather than doing a bunch of cheaper courses where prices add up.