So I need gutters on my house, getting the seemless kind. All the prices are within a $50 space, no big deal, but...

One guy wants to do 6" gutters and 4 down spouts. $1150
Another wants to do 5" with 8 down spouts. $1114
and another wants to do 5" with 6 down spouts. $1130

This is for a 2600sq' house that is perfectly straight on three sides... I'd say I have a medium pitch on my roof.
I trashed two of the quotes (not listed) because the guys were dirtbags and their measurements were a few feet higher on every side than the three listed above.

I want to go with #1 because they have done work for friends, guy drove a nice clean auto, was well prepared, and very professional. He says the 6" with the 4 downs will be fine... 8 seems a bit freakin' much and while they are charging less, seems like they are padding a bit.
All are members of the BBB, 25+ yrs exp, seemless, and lifetime warranty.

ETA: I don't have that much water coming off my house... Just the rear and the front (where the roof meets at different levels and the water fall get pretty heavy.) My yard is getting really jacked up, so I gotta get them.

Without seeing your roofline, there is no way to compare.

8 downspouts seems overkill though

6" is a must, any smaller and the water will wash right over the top of the gutter during those mid-summer gullywashers!

It would be nice if they are licensed, bonded and insured.

Quoted: Without seeing your roofline, there is no way to compare. 8 downspouts seems overkill though 6" is a must, any smaller and the water will wash right over the top of the gutter during those mid-summer gullywashers! It would be nice if they are licensed, bonded and insured.

10-4 they are.

It is good that you have multiple quotes. And the fact that all are expeianced contractors, with BBB listings.
The 6 inch gutters are usually considered commerical and also tend to be of heaverier gauge then the five inch.
If you have friends that have used the services of the first one what are their impressions of the work and his work practices? A craftsman who runs a clean job tends to also pay more attention to the quality of their work.
I have been doing a lot of contractor evaluations and quotes including guttering. Home was hit by tornado in November.