Genotyping reads specific positions in DNA, selected because they vary between people: many are associated with traits or conditions, while others are used to estimate nearby variants through imputation. Sequencing reads DNA letter by letter, in the exact order in which it appears, and Ultra covers virtually the entire genome.
Genotyping is highly accurate for common variants and costs less, which is why we use it for Starter and Advanced. Sequencing also detects rare variants and variants not included on any chip, and generates data you can reuse for future analyses; this is the technology used for Ultra.