One measure of a pangram's quality is its shortness. Obviously in English the shortest possible pangram is 26 letters long, however very short pangrams tend to be nonsensical and it seems near-impossible to come up with a meaningful 26-letter pangram. For example, the following have 31 and 30 letters respectively:

The five boxing wizards jump quickly.

How quickly daft jumping zebras vex.

...and the only minimal pangram I've seen (before Tem42's example above (which some might disallow because of the abbreviations)) is this one:

Vext cwm fly zing jabs Kurd qoph.

As you might have guessed, many of these words are archaic English. The sentence means, approximately, "An annoyed fly in a valley, humming shrilly, pokes at the nineteenth letter of the Hebrew alphabet that was drawn by a Kurd". Now I've always wanted a succinct way to say that.

Source: Weird and Wonderful Words (The Bedside Companion for Insomniacs), Paul Hellweg, David & Charles 1986, ISBN 0-7153-9084-8.