The PVR150MCE is a newer generation than the PVR250MCE and is a bit cheaper for Hauppauge to produce. Other than that, there arn't many major differences.
Personally I prefer the non-MCE variety, which comes with a remote, and the added bonus for the PVR150 is the additional IR blaster which is not included with the PVR250.
I have no preference between PVR150MCE or PVR250MCE. I dont think there is anything significant either way.
i have a 150 and a 350 and the picture quality is a lot better on the 150 than on the 350, and im pretty sure (99%) the 350 and 250 have the same chipset, so i would go for the 150mce over the 250mce.