I have about 60hrs experience in a Katana and only about 2 in a cesspool
172, so cannot really provide a balanced comparison. However my experience of the Katana has been:-
1) As people have said, the Katana handles very well in the air, great viz, great gliding characteristics for those PFLs.
2) Not very complicated, all the knobs, buttons etc are well placed. The Rotax engined types have a variable pitched prop, but again, I've never found this a problem.
3) No problems handling on the ground, keep the weight of the nose wheel if req'd, but I've never really had any problems.
4) As to reliability, I've only had 1 lesson cancelled due to aeroplane going u/s.
As mentioned above I only have a couple of hrs in the 172, but I was genuinely shocked by it at first after experiencing the modern Katana. The 172 smelt like an old A35 Austin van, the doors pinged like them too when you shut them, the viz was awful.
The school that I learn at runs a 172 and a couple of Katana's for students. Generally, it is cheaper to learn on a Katana and then if you want a 4 seater, then to do the necessary conversion hours.
Overall tho', I'd agree with the comment that it would be worth trying out the different types that are available to you before plumping for which one - ie don't just make your choice on cost alone.