Are you a solo learner?
If you are naturally curious, driven, sufficiently motivated, and love to figure out things on your own, then perhaps studying at your own pace would be the road for you to take. Self-study has many benefits as well as drawbacks; each one uniquely helpful or detrimental given the attitude of the learner.
Studying alone is better for people who value being able to:
• Study at their own pace
• Use whatever materials they want
• Learn what interests them
• Flexibility - no schedule to adhere to or classes to attend
• Cheaper - not having to pay a teacher definitely helps save some money
Do you prefer formal study?
Formal study, as I call it, is in a typical classroom setting. The most common would obviously be in a school or university with an actual teacher being paid to be there with you.
Formal study is better for those who:
• Have a hard time staying self-motivated
• Like structure and the additional interaction with classmates and instructors
• Want correction and help with difficult things and would prefer not to spend time looking up answers someone else already knows
• Isn't necessarily trying to learn the language as fast as possible and perhaps enjoys the journey as well as the end result
A lot of people who learn on their own don't necessarily want to bask in the fun of learning a language; they just want to learn the language as fast as possible.
Another thing that may play into your decision could be what your end goal is. If your end goal is to simply be able to speak a few sentences on a trip to any English country, it may not be worth the extra money and time commitment a formal education programme would require.
However, if your goal is to someday become a foreign language teacher yourself, you may want to get into the classroom groove in your own studies; a degree is also required to actually teach foreign languages as a professional educator.
Whatever your reason, additional languages only enrich your lives, regardless of how you learn them. One of my favorite optimistic quotes is by Lucille Ball:
“One of the things I learned the hard way was that it doesn't pay to get discouraged. Keeping busy and making optimism a way of life can restore your faith in yourself”.