Each chin is different ... some prefer loose hay and others seem to like hay cubes best.
Easiest way to decide which one to give him is to see which hay is the base for his pellets. If Alfalfa hay is the base, feed Timothy hay. If Timothy or any of the other hays are the base ingredient in his pellets feed Alfalfa. Both hays have different qualities that are good for your chin. Both hays are available in the bale/loose hay form, if he seems to like the texture of loose hay the best. Often the availability of one or the other is the one that decides which you give your chin.
Almost all chins like the loose hay ... it's easy for them to handle and easier to chew.
With the hay cube, break it down to layers about 1/4 to 1/2 in thick ... he may like it better because he will be able to carry it around the cage and handle it much easier. If that one cube has been in there a week, I would just dispose of it ... good chance he may have wet on it ... that could be the reason he is not eating it. If he reacts to the new cube the same way ... then it is one of two things ... he likes Timothy best ... OR ... he likes the texture of loose hay best. Trial and error is often the decision maker.
If a chin is sick, I give them loose Alfalfa hay.
I do tend to give the kits, pregnant moms and nursing moms the Alfalfa hay, for the extra nutrients.
Once a chin reaches 3 months of age I usually mix it half and half.
Once a chin reaches 6 months of age, I usually give the non-breeding chins Timothy hay.
If one or the other is the freshest ... go with the freshest one available.
Jo Ann