Both of these hosts provide a great service. I do have to give the edge to SiteGround, but if the cost was a factor I would recommend A2 Hosting all day long. You get more bang for your buck with A2 Hosting and the performance of the hosting is near identical. Also, keep in mind that SiteGround is metered hosting, so you have to choose your package based on expected monthly visitors which can be a huge negative. SiteGround is more WordPress focused and it's no surprise why they have such a loyal following.