I just did a quick test:

First Test (for loop)
I used the string 'talkphp' and looped each method 300000 times in a for loop.
rounded to 3dp

SHA-1 : 0.349 //average
MD5: 0.307 //average


Second Test (while loop)
I used the same string and loop number, but i used a while loop as it seems to be quicker than for.

SHA-1: 0.343 //average
MD5: 0.301 //average

MD5 is slightly quicker on my machine anyway, ill do some indepth benchmarking in a mo.
Ill test others too, apart from base64 coz its 2way.

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mysql> SELECT * FROM `users` WHERE `users`.`clue` > 0;
Empty set (0.00 sec)