Purely a personal choice - Aperture is less expensive and has totally integration into the Mac OS and other programs, PS does not - PS is a more powerful editor and a less powerful photo manager
Is a Ford better than a Chevy? Is a Mac better than a PC?
Only you can deciede
And if you have Aperture questions then the Aperture forum is a much better place to get information - this is the iPhoto for Mac forum
That is a bit like asking which is better a wrench or screwdriver.
They are different and do different things. At their most basic, Photoshop is a photo editor while Aperture is a Aperture is a DAM ( Digital Assest Management ) tool. So while Aperture stores your photos and let you do some adjustments to them, Photoshop has more powerful adjustments but no storage capablilities.
I asked that your post be moved to the Aperture forum.
Or the old standby BorderFx there is an iPhoto version as well as an Aperture version.
I agree with Terence. I'd go the iPhoto BorderFx route to start. You could always move up to Aperture if you need the extra power down the line.
Photoshop, in my opinion, would be added after you setup your data management using a DAM like iPhoto or Aperture and found you required the ability to do editing that a PS allows. And once you're at that point take a look at GIMP a free editor much like PS.
Photoshop is a massive, expensive, difficult to master compositing engine for producing graphics files. A subset of that involves preparing digital photographs for publication.
Aperture is a large, sophisticated, moderately difficult to master digital darkroom for storing, organizing, preparing for publication, and publishing digital photographs. It does not allow compositing.
Each -- at Terence points out -- is enormous overkill for the needs you state. I second Terence's recommendation of iPhoto and a watermarking app (though I don't use iPhoto and don't know much about it).
I, too, recommend BorderFX. Forgot there is an iPhoto version. h/t Frank.