Considering the options you mentioned,
I would compare the pros and cons.
Finding someone who will work with your pre-purchased product may take some searching. You'll want to make sure they have good experience laying your brand of floor…. and it will be harder to discern ahead of time whether the price/quality (ratio) of workmanship will be to your satisfaction.
Will they return if there is a problem down the road?
Sometimes the independent guys are here today and gone tomorrow…. but it could work out splendidly and be the preferred way for you!
Using the big box to provide and install may afford you more of a guarantee or warrantee. Are the installers employees... sub-contractors?
I have done 'big box w/installation' in past homes. Worked well, but required more physical involvement for me… and no substantial savings, really.
Using a local, well known flooring company (and their own installers) is rarely a wrong choice. All you have to do is pick it out, then get out of the way.
There are many companies (with good reputations among Villagers) who carry identical brands or similar products- and most will give you free estimates- so you can easily compare costs, time frame, etc. from one company to the next.
I've had good experiences here.
In my opinion, really is a matter of personal preference.
