The purer the better. You can get 99.98-99.99% purity. Lesser pure types tend to cause more of a garlicy type smell, the less pure it is the more you will notice the smell.
I purchased some which is claimed to be 99.99% pure and made in the US where the best DMSO comes from. Avoid stuff which is made in China.
Read about the cautions on using it before opening the bottle! It's a solvent so needs to be used very carefully. Don't go splashing it all over yourself as it can take anything on the skin, into the skin.
I suggest that you read up thoroughly on it before using it.