I don't really know much about the 738, but I just bought my wife a taurus pt709 which I am still runnign through the break in process. It has features that could have easily made it my preferred carry gun if I had not already filled that slot with a glock 36.
I have read a review on the 738 that was very positive. I have also never seen a bad review on a keltec. I have read a few complaints about the ruger, but they seem to be pretty generic to the type of gun it is, too small and hard to get a grip on, sights are too small, etc. I am sure this is true of the 738 and keltec also, I have never personally owned or used one of them. I have had good luck with taurus products that I have purchased. The only gun that I ever needed to send back to make it work right was a ruger mark II. They did make it work right, (by replacing it) after the second trip to the factory, but it does work great now.
I personally would buy either the ruger or the taurus without thinking twice about it.