The problem with letter scoring is if you end up on averaging sites, your letter grades are up for interpretation. A C on metacritic is a 50, while on gamerankings it's a 65. Personally I think a C should translate into a 70-75. There's a lot of discrepancy.
Letter scores or TWRoO's system are both good if you don't care about averaging sites. Otherwise the 1-10 scale with .5 increments is decent without trying to be too accurate.
Maybe even something along the lines of a "between" score. It would take away some of the inaccuracies of giving an absolute score while giving averaging sites a good idea of how to list it.
For example, Resistance 2: 80 - 85