The bootlegs have clocks and terrible subtitles, if you can even find them for sale anymore. Cropped image, converted from AVIs ripped from Japanese TV.
The Japanese version has no English audio or subtitles at all, and it's really expensive.
The Korean version is one of the best, with dual audio and subtitles iirc, but they only released half the series.
So that leaves the Australian version and the US version. The Australian version is stupidly expensive, but has a great widescreen picture and nice packaging. It comes on 12 individual discs, but you can also get the last 6 discs ("season 2") in a single 6-disc casing. Nice artwork. The US version is cheap, but you get a cropped 4:3 image and it comes in 5 slimline cases in a cardboard slipcase. No special artwork. Both versions have the same DVD extras (ie. not much).
I'd say go for the Australian version if you're really into it, but get the US version if you're just a casual fan or don't want to spend much.
Places to get the Australian version:
Your local ABC shop might have a few leftover copies. I got mine for $10 per disc.
Big W might have some too. I picked up the 6-disc casing from there for about $50.
EBay is another good place to get them, although there aren't any listed at the moment.
Online, I could only find two places that list them:
https://www.play4me.com.au/product/astro_boy_volume_1_566956_191261.html
http://www.bigwentertainment.com.au/product/astro_boy_volume_3_572920_191261.html
And they're both unlisted/out-of-stock. But they're $20 a disc anyway, which is a total ripoff. No one wants to pay AU$240 plus shipping for the 2003 series.
Places to get the US boxset version:
EBay (typically US$15-$30 plus shipping for the entire series)
Amazon (US$20 plus shipping)
http://www.rightstuf.com/1-800-338-6827/catalogmgr/HTMc531kG1=lgzlFGw/browse/item/65426/4/0/0
http://www.yesasia.com/us/astro-boy-the-complete-series-5-disc-set-us-version/1004426223-0-0-0-en/info.html
http://www.videocollection.com/product.html?product_id=38011
I've shopped at The Right Stuf and YesAsia before, they're both good.