I use horizontal nipples so they don't freeze in winter. I was satisfied with (and the birds liked) vertical nipples, but they froze every winter, so that's a no go for me.
Either one is fine for dispensing clean water in moderate climates. I honestly don't know how cold horizontal nipples can go before they too start to freeze.
Either one is fine for dispensing clean water in moderate climates. I honestly don't know how cold horizontal nipples can go before they too start to freeze.