The 2 are each very good in different ways. Which were perfectly demonstrated in the derby. Gilchrist is a solid defensive full back, while Seriki is more of a marauding, attacking wing back, who relies on his pace to handle defensive situations rather than innate technical ability like Gilchrist does.
In a match like Tuesday, you can play Seriki with very little concern of the decision backfiring. Our team was competent enough to retain possession for longer periods, preventing Oxford from building forwards slowly, and perhaps forcing a mistake out of Seriki as a result. We can cope with any counter attacking threat with the other defenders, along with Vini, to sniff out any major threats, and force them, as we did a few times in the first half especially, into shots from range.
Tonight is not likely to be one of those games. Sunderland are a much stronger side than Oxford, even while missing a few players (e.g. their left winger whose name currently escapes me). They will almost certainly have more of the ball, and put a greater amount of pressure on our defence than Oxford did. As such, you play Gilchrist. He can sit behind the wide player, and hold a strong defensive line with Souttar and JLT in the middle. He is excellent at one-on-one defending, so should do fine going up against a winger as Sunderland will have. Then there is less reliance on the winger in front of him to come back and defend, meaning you can leave him further forward and force Sunderland into a decision on whether to leave a defender back to watch our wide player (probably JRS), or push forward, and gamble that you won't be caught out on the break.
