Really just depends on what you want and your playstyle. With my playstyle I was looking for the croc and I was prepared to re-roll until I got it. I rerolled my first form and ended up with mongoose and my second form was the croc so I ended up getting what I wanted. With a shifter any combo could possibly be better for exploration, its really a crapshoot. If you went water/defense you could end up with hippo/rattlesnake/walrus which would be an excellent exploration and pk character arguably. It all depends on how lucky you get with the forms.

Like I said though, the only real advantage is your minor forms take less mana to maintain.