I solo as a single bar stamina warden and am a bit uncertain about which ultimate to use. I don't use Wild Guardian often because he does not seem to do that much damage and the bonus bash seems redundant given that I can do more damage myself during the activation animation. The re-summoning animation when he dies is fun but takes too long in a major boss fight.
For really tough bosses I tend to use the Healing Thicket. It makes me robust and I am pretty good at wearing the boss down. Just takes some time and patience.
I also use the mage guild comet quite a bit, but that takes soooo loong to reload and I suspect should really be for a magika based character. I can do Vet Selene's Web with the comet but need thicket for Vet Arx. I don't know if that means the thicket is better for me, or if it is a case of horses for courses.
Just interested what ultimates people would suggest for the warden and what they think of the options.