I'm confused about how exactly I should compute a change for transactions.  
Say, for a given address I have 4 unspent outputs containing 2 BTC each and I want to send 5 BTC to other address.

Here's what I do:

1. Find 3 outputs needed so the total is 6 BTC
2. Now, what should the change be? 6-5=1 or 8-5=3?