depends on your squad
if your squad is comprised mostly of lowly skilled pilots (eg. 7-8 TIEs swarm, 4 ship rebels), you want initiative. it means that you get to move first, meaning that you WILL get to have your actions, and minimize collisions from happening. It also means that you can move into position to block others, ie. your academy TIE can now block his academy TIE and force him to lose his actions, while all of your Academy TIEs now have focus/evades and whatnot to pummel him with.
if your squad is comprised mostly of high skilled pilots, you DO NOT want initiative. This means that Darth Vader / wedge on expert handling is moving last, and they can better aim their rolls/targetlocks/etc since everybody has already moved. This is pivotal against other enemy ships of the same skill level. suppose Darth Vader vs Wedge on expert handling. If Wedge goes last (ie. Vader has initiative), not only does he get to roll out of Vader's firing arc (if possible), his expert handling also removes the target lock Vader had on him, making target locks totally useless on Wedge. If Wedge has initiative and goes first, Vader will now be the one rolling out of his firing arc and doing nasty things to him.
EDIT: IF you have Biggs, and IF you are up against 5 skill level opponents, you really do not want initiative. The ruling is such that if Biggs dies to other 5 skill pointers, Biggs will continue to stick around until Biggs has fired. Meaning: suppose you are up against Nightbeast and Wingedgundark with initiative. one of them fires and kills off Biggs. the other one has to fire at Biggs again, wasting his attack. Then it's Biggs turn and he fires at something and gets removed from the game. If Biggs had initiative instead, Biggs would fire at something, then Wingedgundark fires at Biggs and kills him, removes him immediately from the game, and Nightbeast is free to fire at something else