I would get the PX4. I know nothing about it. It is as good a place as any to start your journey. My first handgun was a Taurus PT101. I really liked it because it could be run SA on safe or SA/DA with a decocker. It was ok, except the non-replaceable front sight was drilled off center and I never bothered to send it back.
In the end, it wasn't 100% reliable with all ammo and I soon decided I had 0 interest in DA/SA guns.
My next gun was a S&W M640. I own and CCW it still today.
If I were you, I might lean more toward Glock, XD and S&W M&P. I say this because these are more popular proven guns and frankly popular things like Glock, 9mm, 40 S&W, 45 ACP, S&W revolvers, Colt 1911's, some Sig model are the standby which are well proven by millions of other people's rounds and testing $'s.
That was more or less where I failed with the Taurus, but it kept us safe for years and seemed to become much more reliable as the round count increased.
In the end, enjoy the journey and the learning.