Low Relief has a slightly larger, lower relief portrait on the obverse ...
NOTE => aside from the size of the portrait, the two varieties have slightly different lettering.
Ummm, I've never heard about the 1948 High & Low relief coins?

... but 1951 & 1952 for sure:
1951 High Relief Quarter = $10 VF
1951 Low Relief Quarter = $250 VF (winner "quarter")

1952 High Relief Quarter = $10 VF
1952 Low Relief Quarter = $10 VF
1951 High Relief Nickel = $850 VF (winner "nickel")

1951 Low Relief Nickel = face value (5 cents)