I am not obvious on the last little bit of your sentence, "which a person is the best". I thought it is analogous into the clause in "I'm planning to include whatever they are", the purchase of item plus the verb is reversed (I forgot what the grammatical time period https://cat-litter-uae56560.tinyblogging.com/5-tips-about-best-litter-brands-you-can-use-today-81225333