I've been on both and I'm still using the Yasmin right now. I took accutane, so I really can't compare what they each do in terms of helping with acne because I don't have many pimples at all now due to the accutane.
Here's what I can tell you about Yasmin. You know how birth control pills are divided by weeks, right? Well, at the end of week 1 and the beginning of week 2 on yasmin, I always get about two tiny baby zits between my nose and upper lip. These are not bad at all and go away in two days. They're not noticeable. I think it must be the yasmin causing them though, because I get them the same time each month. They're not always in the same spot, but are in the same area. I'm pretty sure that they are caused by the hormones in yasmin, but they're hardly a problem. That's my only "complaint" about the pill. There are some really good things about it too. First, it doesn't make me all hormonal and crazy. No mood swings on this pill. Other ones have turned me into a crazy woman. Yasmin, like spiro, is a diuretic, and helps you keep off all that bloat during your period. This pill has helped soooo much with my cramps (sorry for the T.M.I.) and helps shorten the period to 3 or 4 days.
In my opinion, Yasmin is a great birth control pill. If you're going to use yasmin to prevent pregnancy or to regulate your period, then I would suggest trying it. If you're just using it for your skin then I would just stick with spiro. Messing with your hormones by taking the pill if you're not using it for actual birth control seems like a drastic step, especially if you have the great option of sprio. Good luck, I hope some of this helps.