If I were Trump, I would not release them for a while at least for two reasons: Mitt Romney & media would gloat and say, "Look, we made him do it." Also, they might spin the most innocent items into something negative or simply lie about them.
It is disgusting for Romney to imply there are things in the tax returns when he has no evidence to support it. He sunk to the level of N. Pelosi and H. Reid who spread false implications about his tax returns when he run, and we thought it was disgusting.
Huckabee recommended Trump not to release any at all. He had personally experience with this. He thought he was smart to release 20 years of his tax return and that he would get credit for his generosity from the media and political opponents. Instead they nitpick his to death and turn many positives into negatives by lying about what was in it. “Never load the gun that someone who has pointed at you”
Beside, according to Reid, Romney never released his. Romney only released a summary of his tax return. Romney really sunk so low