Have you tried "stage 2" formulas? These formulas are made by all the different brands, and they are designed for older babies and toddlers. The main reason I mentioned this is because they also come in flavors, like vanilla, as well as unflavored. The new flavor may encourage your baby to continue drinking formula for a bit longer. They have many more of the nutrients your child would get from normal formula than soy or whole milk. I think most of them are marketed for ages 9 -24 months (some are now labeled 9-36 months). I would try one of these "older baby" formulas before moving on to whole milk or soy prior to 12 months of age. If this doesn't work, you might also try 1/2 and 1/2 formula and whole milk or formula and soy. The main reason to not feed whole milk to babies younger than 1 year is that whole milk is deficient in nutrients essential to brain development, while breast milk and formula include these vital nutrients.
You also don't mention the route you are offering these drinks. Sometimes offering a sippy cup instead of a bottle can get your child "re-interested" in drinking (or even assisting them to drink from a "real" cup like a dixie cup). Also, make sure you are still offering the formula/breastmilk prior to a solid feeding at this age. Some times the stuff in the bottle is not the issue, it is just that the child feels full.
If you are still breastfeeding, I know many BF moms who have said that they have to get away from the action to BF at around this age - high level of stimulus can make eating seem like a low priority to babies at this age.
Most children who are allergic to milk will also react to milk based formula (I am allergic to milk, and my mother found out by weaning me from breast milk to milk based formula), so unless your child has had problems with milk based formula, I would start with whole milk rather than soy as dairy has nutrients that soy lacks.
Sorry to be so long winded, but I hope this information helps!!!!! Good luck!!!