Without going into the specifics of operating costs which would be broadly similar between the two types, I would say go for a C152.
C152s are more common, as are the airframe parts to repair them - some PA38 parts are getting scarce to source - even flying control cables, nose legs etc. The engines are essentially the same bar no mechanical fuel pump on the C152 but you do get (normally) dual impulse mags and an accelerator pump on the carb.
C152 value will remain stable or even increase. PA38 airframe (wing and associated structure such as the carry thru spar) hours are lifed at 11000 hrs. Although life extension mods are available it isn't really worth the expense.
Engineers will be more knowledgeable about C152s due to them being more common.
On the flying side, C152 is far better for 'short' field operations.
No doubt you can find a PA38 for less than a C152 - the ramblings above might indicate why...
An alternative for hour building which would probably work out cheaper in the long (or even short run if you're unlucky) run than owning would be to lease a good aircraft from someone with a good reputation like
Big Red Kite Aviation.