Newbie wants to buy a bike, but which one ?

[Rogering]

Hi guys.

I haven't ridden for many years & now the time has come, but what type ? your valued input is appreciated.
Basically want to ride casually a few km's every week on mainly on pavement, road & maybe a bit of dirt,the landscape is mostly flat but the hills can be a bit tough.
I've been to the local bike shop & had a look at Malvern Star Switch 29-3 & 29-5 (I'm male under six foot).
Am I on the right track regarding the type of bike? any specific brands that I should consider around the $500 -$600 mark

many thanks