Either one would be fine but only one. They can both happily live their whole life out in a 90. I do not know why others think they can't. Their max size is only 9 to 10 inches. A clown, queen, blueline, niger and some others get upwards of 18 to 22 inches and need a much bigger tank but either of the ones your thinking of as i said can live out their whole life in a 90 no problem. I have keep many triggers for years. For good, interesting tankmates that should all be added first or if not i would take the trigger out and rearrage all the rock work and add the new one and give it hour and then replace the trigger in, would be lunar wrasses, yellow tang, v-tailed grouper and harlequin tusk to name a few. All could live their whole lives out in a 90 as well i would say the tusk would be best off in a bigger tank in the end though.