anything with a wanted label gets sent to abyss that's all you need to know in a RES, Scan them with the KWS if they're a M ship or above, anything smaller isnt worth it when there are other ships to be dispatching (takes longer to scan them than kill them) - Besides you'll just end up with a cluttered transaction list full of unclaimed bounties in random systems (perhaps they will "fix" this in 2.1

).
if its a wing of 2, target the smallest, they will be dead long before the larger ships knows what the hell is going on.
If its a wing of 3 depends how confident you are, i would open fire, picking off the quickest kills first.
a wing of 3 NPC conda's well again i find this fun, others may not. (asteroids are your friend here, condas can't pilot through them that well)
a decent RES should be target after target until you've had enough i normally spend an hour in a HAZ RES before jumping back out to claim roughly 2-3 million credits depending on what targets were available
Low RES - mainly small / medium ships, plenty of security vessels to help you out too
High Res - mainly medium ships some large not often though, less security but still sometimes they pop up, NPC's tend to be deadly or above in rank (i.e they carry some decent modules rather than just a pulse laser and a bag of crisps in their class 6 slot)
HAZ RES - Mainly large ships or FAS/FDS, no security but each ship has easy 100k or above bounty on their head, NPC's can be elite and are obviously better equipped and better pilots
on larger ships target the power-plant subsystem you can kill them alot quicker