Genesis 15:6

"he trusted the Lord, and he reckoned it to him as righteousness". There are basically three ways to interpret this crucial verse:
(1) the Lord reckoned to Abraham righteousness [that is, the righteousness is Abraham's, the righteousness pertains solely to Abraham and his standing with God].
(2) Abraham reckoned to the Lord righteousness.
(3) the Lord reckoned to Abraham righteousness [that is, the righteousness is God's--it does not pertain solely to Abraham but can be lavished on others on account of Abraham's trust].

(1) is the standard evangelical reading. Abraham believed God and God reckoned him as righteous. This is usually [but not by James-see below] understood to be that righteousness is something that even a believing Abraham did not deserve before the reckoning. The problem with this is that there is nothing to prepare the reader for this interpretation. There is no distinction made between "belief/faith" on the one hand and "righteousness" on the other.
(2) would mean that Abraham trusted God and thought that God would fulfill his promise, that is God is righteous. This is possible. However, this is not how the LXX understood the verse and is also not how a similar verse is interpreted (Psalm 106:31).
(3) would mean that God merited to Abraham righteousness in the sense that God would benefit Abraham and Abraham's seed on account of Abraham's trust. This interpretation makes sense of Genesis 19:29 (if God remembering Abraham has in mind Abraham's credit-meriting trust/faithfulness) and it makes sense of Genesis 22:16-18 and 26:3-5 (Paul used 15:6 because at that time Abraham was not circumcised; he did not use 15:6 because "trust" is different than "faithfulness").

The importance of these differences is huge. If one adopts the usual construal of (1), then Abraham's trust is mere belief and the righteousness he has is undeserved and therefore imputed. This is how evangelicals read Paul's gloss on Genesis 15:6. However, if one adopts (3), then there is no separation between faith/works and that Abraham's trust is on par with his faithfulness. God's righteousness is then had by grace by those who benefit from Abraham's merit-earning faithfulness. This interpretation is then used to better intepret Paul and his entire theological enterprise (along the lines of the "New Perspective").

James' correction of a possibly early misinterpretation of Paul concerns how one reads the "trusted". James read it as faithfulness and not mere belief, which would go hand-in-hand with (3). However, it is unclear what for James "righteousness" entails. Is it solely for the individual [in which case James holds (1) but not how that is usually understood] or does it also involve merit-earning righteousness for others. From what James says it seems that righteousness pertains to the individual (Abraham, Rahab, or anyone), but there is no reason why he thought that it pertains solely to the individual, especially in the case of Abraham.

Therefore, my bet, if i were a betting man, is with (3).