I would suggest the second most recent version of the current stable release (7.23 at the time of writing).
The only reason I would not suggest the very latest is that sometimes a serious issue is found and that version is withdrawn. If that is the latest version, you can’t roll back to an earlier version. I have been caught out on this before.
The exception to this is if there is a bug fix or feature in the latest version that you really need.
On the one hand I would always recommend updating to the newest Mendix version, so you have all the newest functionality. On the other hand when a Mendix version has just been released it's prone to have a few bugs which are not yet found. If a Mendix version is out for 2 weeks it's likely to have most bugs fixed in patches and therefore stable.
With that said I would recommend 7.23.6 (build 53654) of the Mendix Studio Pro.