you can say either "요" or "여" but, pricisely speaking, it is advisible to use "요" as "여" is not a proper word. Language constantly changes over the years and the dawn of "여" comes originally from users using the internet aged under 20th (this is my guess). This is why it is not commonly used for a daily life but on the internet. "여" is also used to express cute and frendship to someone you don't know. Again, use "여" on the internet only ^_^

둘다 괜찮아요 :) me too.."요" Difficult to pronounce 음..그렇지만 but.. ex- 안녕하세요 --> standard 안녕하세여 --> buzzword for internet? hehe xD more- 식사하세요 / 식사하세여 함께해요 / 함께해여