I'm speaking from personal experience and I'm saying all these in the external flash context.
I feel that either you get a cheap 3rd party one or the flagship first party. It'll save you the upgrading cost in the long run, should you feel the need to get a better flash unit in the future.
A cheap one will allow you to experiment and find what you really want in the flash. E-TTL, high speed sync, wireless flash control, power, stroboscopic etc. For a TTL one, the YongNuo YN465 can be had for around 100 bucks, iirc. Use it, learn it, outgrow it, upgrade. The manual YN460 is even cheaper if you will.
If budget is never a problem, why is there a need to consider cheaper alternative? Just get the 580EXII and it'll last you a very long time.
Sure there is the other side of the story whereby you are contented with your YongNuo. That's even better, cause' you only spent 100 plus bucks and it does get the job done for you.
Some food for thought.