Howdy @lincolneas - It really depends on how you intend to use the flash, on-camera, wirelessly or using it to control other flashes. If you want an external speedlite to grow into, the Canon 580EX II (see here) would be the best choice if you have the budget for it. It's Canon's most powerful flash and comes with advanced wireless master control functions, great for shooting off-camera and for controlling other speedlites.
If you don't intend on using the master control function, then the 430EX II (see here) would be the next best choice. It will give you wireless capabilities for shooting off-camera and is powerful enough for group shots and for bouncing light in medium sized rooms.
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If you don't intend on using the master control function, then the 430EX II (see here) would be the next best choice. It will give you wireless capabilities for shooting off-camera and is powerful enough for group shots and for bouncing light in medium sized rooms.
Hope that all makes sense and happy shooting! :)