~ 요 is also formal but it's softer way and less formal than ~습니다. But ~요 form is mostly used by Korean natives these days in normal circumstance. So in school when Korean teachers teach foreign students, we always teach with ~요 form. There is another form which is not formal and casual. You can learn that from my blog. You will see clearly. :)

umm.. thanks Doris and CoreanBig sis ... but in all times.. if I change -습니다 by ~요 .. go to the FORMAL for INFORMAL?

Doris was correct. But also -습니다 could be a bit too formal or dry to talk in personal. So if it's normal circumstance like meeting new friends, we just use ~요 form. Because it sounds softer. www.coreanbigsis.com

It should be "만나서 반갑습니다" when you first meet someone,I think. ("반갑습니다" shows more respects than "반가워요"^ ^)