Its just personal preference... neither box is better than the other; as they both do the same thing.
Nokia's tend to have tuner problems, whereas Sagems tend to have power supply problems. Its hit or miss with any box you get.
And also, you'll find no difference in performance in a 1x OR 2x box; same goes with AVIA500 and AVIA600 - they are just different chipsets.
Hope this helps.
Liam.