5-10 for me.

And like Ryllharu, I usually try to finish 26-episode series in one day. It depends on what time I start watching it, so if I start in the afternoon one day, I'll finish it the next day. If I start in the morning, I can easily finish it in one day. I can't stand to watch 1 or 2 episodes a day when the entire series is sitting on my hard drive just begging to be watched. 50+ episode series take a bit longer. It took me about 3 or 4 days to finish FMA and Gundam Seed.