For a deletion you should go for at least two different guides. However, you need to keep in mind that guide cutting efficiency may vary, so you will need to make sure that both of your guides (if you go for two) have a decent cutting efficiency. Otherwise, you will need to design and test more guides.
For the exact and precise deletion a two guide RNA will be best option, would be great one guide on the (+) strand and the second on the (-) strand. Each guide can be tested separately with T7E1, once the cutting efficiency confirmed , both guide, and cas9 (three plasmids) can be co-transfected on your cell lines of interest.