Any version of Joomla is fine.
There are a few minor differences though:
on joomla 1.7 the ACL fine tuning is better and doesn't require any other extension to setup the user groups.
on joomla 1.7, you don't have joomfish yet, with which we integrate for multi language. So you would need to stick to joomla 1.5 for now if you need that.
on joomla 1.7 the translation library is locked down and we can't override translations in the back end and in emails. That's not a big issue, and you can go around the problem, but still.
On our end, we still use joomla 1.5 for our website and our demo website mainly because of joomfish. Once joomfish will be compatible, we'll probably switch to joomla 1.7 or 1.8