Hope you do well with making your quilt.
There are a couple rulers that I consider essential and will work for most every task. Those are a 6" square, a 6" by 12" ruler, a 6" by 24" ruler, and the 12" square ruler. That said, I have a big box of rulers, probably because I like my toys as much as the next quilter. There are two favorites, the BlocLoc rulers and the Flying Geese X 4 ruler by Lazy Girl designs. The most despised ruler is one I bought for a class and hasn't been used since. Next time I'll just skip the class if it requires another new ruler.

For my first few quilts I got by just fine with my 12.5 square, a 6.5 square, and a 6 x 18 rectangle that I stole out of my mother's stash. I have acquired a handful of other rulers since then, but those three are still the ones I reach for the most. As for specialty rulers? The two I use the most are a flying geese ruler, and one specializing in cutting triangles for HST by the finished size. Takes the pain out of cutting fabric by the eighth of an inch and saves fabric in the long run. Every other ruler I have I purchased for a specific purpose and haven't touched since that project was completed. Now if they tell me I need a specialty ruler and I can't figure out how to do it without one, I find another project.

I agree with what Origami said. Those specialty rulers are so pricey. I have a couple still in their wrap and wish I hadn't bought them.