What opera tenor fach is considered a low tenor and a high tenor?

From lowest to highest, you've got:

Bariton-Martin, or baritenor--kind of cheating, because this is more a baritone fach, but sometimes they sing tenor rep; next would be either a heldontenor or dramatic tenor--huge, dark, but not usually super high voice, or a character tenor--usually a smaller, brighter voice, also usually not too high; then you have spinto tenors and lyric tenors (lyrics are just a little less big and brassy than spintos)--both of which are clear, clarion sounding voices, both singing often up to high C; then you have leggiero tenors, who have the lightest, sweetest tenor voices, and sometimes sing as high as an F above high C (Google Juan Diego Florez singing "Ah, mes amis" for a lot of high C's and a high D). There are a couple of other minor fachs in there, but those are the main ones. Hope that helps :-)

Generally the more lyric voices sing higher while the more the more dramatic end of the spectrum sings lower.