Verified answer

Interestiing and challenging question that is very much grist for my mill!

In a spoken context I would say both are right because both are clear and unambiguous.

From the point of view of logic, I agree the second is more, let's say, consistent.

However, in a slightly more formal written context I would prefer the following:

"The service that they povided our business was the absolute best."

The present perfect would only be acceptable if the phrase was said with a time expression like "in the last 20 years."

The style of the sentence is slightly careless and inadept. It seems knocked off without too much care.

"Our company was provided with impeccable service." For example would be clearer, crisper and more precise.

The sentence "The service they’ve provided our business is the absolute best." is correct. It implies that their service is still the best (still in the present) if you use has been' that would imply that their service is no longer the best, while in this case it still is. So the use of the present tense is correct because they are still using something that it has been given to them in the past although they still currently use it.

Hope this makes sense and helps

Your first sentence is correct. It uses present perfect to show that your company was serviced by these people numerous times in the past up to now. It also states that in general, and over all their service is fine. The quality of their service does not fluctuate, and it is one single way of serving, while you have had multiple services from them.

i think youre right

have is past tense because they said providED

but the service IS the best,

i'd still say it needs to be, HAS been, since they already provided the service