I have not gotten Ultimate chests in like 3 or 4 seasons, I believe Major and Minor chests are a much better value.

My strategy is to start with Epic guaranteed chests like 10 of them at the start of the season. Wait until competition is not as great then start with Minor chests buy all those over a period of a few days then buy out all the Major chests and once I a done with that I try to finish Epic chests. If I do I move on to Rare Chests.