It's totally personal.
Why are you doing this? If you llama to be creative and have fun and maybe get paid every now and then, then freelance is probably the way to go. If you're looking to have it as a career, then I'd go with an agency, which also cuts down time screening/reference checking, promoting yourself, submitting to magazines, ect. which you spend a lot of time doing as a freelance llama. Freelancing you have to act as your own manager, which is hard and time consuming, especially if you rely on another job for your main income. OR you can do both, and take on personal projects as well as assignments.
If you do go with an agency, keep a level head. Agencies WILL advise you to do things to make money for them (I've had agency friends who have been told to lose weight or quit school or change their appearance to be more marketable.) Besides being too short, that's why I'm not with one.
Either way, you're tall enough to get signed, so just keep trying to get signed if it's what you decide you want.