Keyclone and IS both are good options. If your using multiple pc's then keyclone might be a good option, however, other than wow, I have run into issues getting keyclone to function with out IS's lock forward option.

If you have to use both... might as well use IS.

Keyclone is SIGNIFICANTLY easier to setup... however, if your comfy with setting up macros, reading text files, and tweaking your setup manually with people who are more than willing to help (lax and his group in MIRC are badass) then IS is much more powerful than keyclone and can do everything it can and some a bit better (Pip switching).

Regardless, its personal preference, but the main thing is.

Keyclone
Pro's
#1 Easier to setup
#2 Cheap price
#3 Well documented

Cons
#1 doesnt work as well with non wow apps due to no lock forward feature
#2 Requires contacting keyclone if you have switch pcs / reformat
#3 One liscense per pc

IS

Pro's
#1 Works with every game
#2 One liscense per 5 pcs
#3 Extremely quick clone switching (pip)
#4 Liscense tied to a log in / pw so reformats and new pcs are not an issue

Cons
#1 Setup time is longer
#2 Setup is requires editting text files and customizing your setup
#3 Documentation can be spotty. (however they have a MIRC with people to answer questions)

I use both...

Keyclone for easy setup, IS for guaranteed functionality and quick switch between clone windows.