Difference between 7446,47 etc
'46 and '47 are for common-anode LEDs, whereas '48 and '49 are for common-cathode LEDs.

For the common-anode types, '46 allows a higher drive voltage than '47.
For the common-cathode types, the difference between '48 and '49 is that '48 has "ripple-blanking input" (for suppressing leading zeroes), which the '49 has not.

There also are '246, '247 and '248 types that work like the above mentioned ones, but use a slightly different display pattern for "6" and "9" (namely with "tails").