I bought a thumbhole. The straight pull on the trigger allows for more precise shooting. For the applications I bought this particular gun for that is better. Most target rifles are either thumbhole or McMillan A4/A5-type "tactical" stocks which allow thumbhole-type holds.
The downside is they are not quite as handy for impromtpu hunting use. If I shoulder the gun quickly I tend to get too little eye relief (ouch!). Large gloves can also be an issue in cold weather.
If I wanted a gun for woods hunting or where the majority of shots would be offhand or withing 100 yards, I'd go regular.