I believe UDF 2.50+ is the 'norm' for the latest generation media (HD DVD/BD).
Being a data disc, it doesn't matter too much though.
Just be aware that XP doesn't support 2.50 and won't be able to read what's on the disc (without an extra little driver).
If in doubt, select all 3 (ISO9660, Joliet, UDF 1.02). That'll give you the most readable disc possible.
UDF 2.50+ have new features that help with recovery should the disc get scratched. It keeps 2 tables of where everything is stored - one at the start of the disc and another at the end (well, after all the file data).
I certainly wouldn't ONLY use ISO9660 (with relaxed restrictions), just use Joliet/UDF which were designed not to have them in the first place.