The commissioners may let the work in sections, or they may let different kinds of work to different contractors, or they may let the whole to one (1) bidder, if in their judgment it is to the best interest of the taxpayers to do so; provided, that after having examined all bids and after having thoroughly investigated the methods of other counties in the state or elsewhere, where conditions are similar, a majority of the commissioners may be of the opinion that to accept none of the bids would be to the best interest of the county, and they may resubmit to another bidding; or, in their discretion, they may adopt any other method of letting the work, either in whole or in part, as the results of their investigation and judgment may indicate.