Right now, I'm using Primo 2.4 (188.8.131.525512). But I was using iGo8 for a long time before switching to Primo for good. iGo8 is the fastest, smoothest GPS app for my 2DIN head-unit (a Rosen GM1010).
Primo speed is perfectly acceptable though - and it has a lot more features that I do like, so I'm using Primo now and will stick with it unless I run into major issues. iGo8 is just faster and smoother on screen updates in the 3D interface (which is what I use 100% of the time). Primo screen updates are a little less "fluid". But since you don't normally sit there watching it anyway, it's not really a big deal....
I still prefer Loquendo TTS though - voices are just more natural sounding - and since I recently found that newer versions of iGo 2.4 (such as 405512) also work with Loquendo voices, I'm pretty happy with Primo now (currently using Loquendo 7 TTS with it).
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