Well, it really depends on the kind of druid you want to be.
If you want to be able to take the hits, go with Doomguard. If you want to give the damage, go with Inferno.
I went Doomguard because I 1) wanted to take the hits and 2) thought that the Doomguard form had -less- disadvantages than taking the Inferno form. If you pump STR, INT and MND and go Doomie, then you'll be able to do more damage, -and- crit more often while having stupidcool defense.
Though, I won't knock Inferno and say that I wouldn't be interested to try him, and Doomie -is- very very slow ( I was spoiled and knew him before the patched fixed his speed to work properly). So Doomie works better in groups, and I assume that Inferno would work better if you do more solo.
But I will say that Doomie has definitely saved my life, and other people sometimes ^_~
If you want me to post my build for Reliea, I'll do that so you can see ^^;