Best Option for Charging a High Voltage Capacitor?
Is this a hobby or a design job? If it's just for you, go with the 555 circuit you listed...it's simple and will really help you learn the basics behind power electronics if that field is new to you. 

If this is for work I'd recommend the LT3750. It's a great controller that simple to use. I've used it in a couple projects in the past. Linear has a great demo board available that will charge these caps in a few seconds. It's free for any company with a relationship with their local App Engineer (just call and introduce yourself) or $125 otherwise. 

If you use this part I'd definitely recommend looking on coilcraft for your flyback transformer, they've got some good ones!