SkyTest is definitely the most accurate in comparison.
For the Maths element I used both Pilot Aptitde and Latest Pilot. The questions on Latest Pilot are more like what you will get but it will be delivered in the style of the Pilot Aptitude version.
I'm hoping to re-attend later this year and I'll be using all three again.
If you use SkyTest I would really let it push you by using the training assistant feature. It will really push your ability and you'll find the actual on the day test is easier than this.