The very best starting hand you could hope for is 4 of a kind.
Unfortunately, you have only about 1 chance in 20,000 of being dealt quads in 4 cards.
Excellent realistic starting hands for high includes trips, two pair or four to a straight flush. Each of these are just one board card away from becoming a huge hand. Four cards to a flush is also a decent starting hand, while four cards to a straight is typically not worth playing, unless it can be played for low. With the exception of starting with trips, having just 3 cards to these hands will require the help of 2 out of 3 cards from the board and that is more difficult. But, if they include multiple possibilities like a pair or 3 low cards, they may be worth playing.
Excellent starting hands for low are obvious: 4 cards of 6 or lower. Such a hand will also include straight possibilities, vulnerable though it is. Having 3 to a flush (including the ace) gives an additional possibility.
Three low cards, all 4 or under, is a decent start, but will take help from 2 of 3 of the board cards. Unless you have other possibilities for high, having just A2 is not a reasonable low hand as it requires 3 nearly perfect board cards.