It really doesn't matter. Because you're cutting with the burr, anything less than 90 degrees would work. Many traditional scrapers have a bevel of 65 - 75 degrees. A skew can be used as a negative, showing that you can use a bevel of much less than 65 degrees.
The advantage of using a "duller" bevel angle is that there is more metal supporting the cutting edge, which can reduce vibration and might increase the durability of the edge.. It also takes less time when originally shaping the scraper since less metal needs to be removed.
The advantage of using a "sharper" bevel angle is that it gets the heel of the bevel out of the way, making it easier to get into tight spaces.