InstallShield and Wise is the leading products out there and which one to choose is a question of personal choice.
They both do their job I guess but has its cons and pros.

I think it also depends what infrastructure you are required to support. If you like many still will support XP for some years(!) then theres really no big reason for you to move from WPS 6.1 which does what you need. Build your knowledge and learn the basics so that you are not dependant on the tool when you get to the point where you migrate beyond XP :-)

That said I've worked extensively with both products and I would not hesitate to recommend Wise over Installshield. This is mostly due to how Installshield historically has extended the msi "format" through custom actions in less flexible and maintainable ways than the Wise product.