Independent lawyer or law firm?

There should be no disadvantage, it all depends on how good each lawyer is. You may find out the price by asking them how much they charge.
There is no telling which one is higher or cheaper, as people's decisions to establish their fees are not in relation to whether they are independent or not. They all charge per hour, as far as I know. You might want to look for someone who is effective in producing results and efficient with their hours, however, there is no telling if that person may be providing services as part of a firm or on their own. The best way is to consult them and form an opinion about which lawyer you would like to hire, regardless of their practice status.

It is not so much a "reduction in fee" that you should "expect", however it is usually true that larger firms charge a higher price because they have larger overhead - their offices are obviously larger, they have a larger staff, and the like. Your most important factor to consider, however, is the expertise, experience, competence, service that you will receive. If you are satisfied/comfortable with the independent attorney, then go for it - good and comfortable relationships are difficult to find, so if you find one, keep it.

Define "independent" and "law firm." There are very experienced, and expensive, independent attorneys, and ramshackle "law firms" with little experience who may yet take your case on the cheap. There is no fee reduction to be expected; no independent attorney will be discounting fees simply because he or she is a solo practitioner.

The general advantage of engaging a law firm is that you will have access to the firm's resources: multiple attorneys and support staff, of course for whom you will be paying. An "independent" attorney may not have some of those resources immediately available but, if nonetheless acting competently, will be able to acquire them if necessary. Furthermore, the nature of services being provided (e.g., transactional services) can obviate law firm overhead entirely for which you will be at least indirectly paying.