Letters of Recomendation

Hi I am a junior and now is the time that I have to ask my teachers for letters of recommendation. I was wondering if it is OK to ask teachers from my sophomore year for recommendations? My favorite teacher is from tenth grade and I think she would write me the best letter. People keep telling me that the letters should come from teachers of my junior year. Would asking a teacher from 10th grade look poorly? Also, how important are letters of recommendations?

Please let me know.

I think you can ask any teacher for recommendation letters, regardless of what year you had them for. And it would be best to ask the teachers that know the most about you.