If you go modular, you won't have to make tough decisions like this one.

Seriously though, it depends on what you plan to play with it.
For games like Battlezone, not having a topfire would be a pain.
For games like Cloak and Dagger, it helps to have the fire button right there, but is not necessary.
For most other games, I prefer non-fire button joysticks (Wicos and T-stiks notably) for their feel.
I'm not really fond of the feel on the Happs joysticks.