I believe that if you are fully confident in your abilities to rape the level you are at, then buy in for the max. Loosing your buy-in to a bad beat should have no bearing on your buy-in amount.
If you are making some questionable calls, then dont buyin for full amount until you improve that leak a bit. If you are regularly getting your money in ahead then go for full buy in...
At PS 2nl, I buy-in for 150BB ($3) b/c I am not confident to call an all in with the full $5 buy in plus that amount is not justified with my BR. Once I get over that, then it will be full buy-in...

It also depends on the tables. If 6/9 players have $2 or less then a $5 buy in isnt all that important.

Thats my 2nl cents.....ouch that was a bad joke...