Personally, I'd recommend buying a license direct from cPanel.
I did a little research into this when I was looking for my own license. I found, of the resellers I checked, that many offered licenses:
1) with support and often at the same price or more that what you'd pay direct from cPanel
2) without any support or very limited support and less than cPanel themselves
I didn't want to risk having insufficient support - things will work fine most of the time but when they don't, having good support is essential. The support I've received from cPanel has, in general, been very quick and straight to the point. The only times cPanel support have let me down is when I've asked quite obscure and odd questions regarding the inner workings of their product (required for development purposes). However, I've always managed to figure out the odd and obscure things given a little time.
Another point worth mentioning is that if you have a cPanel account, you'll receive (occasional) emails direct from cPanel concerning important security information, such as 'must have' patches and so forth. If you get your license through a reseller, the reseller will be sent this information instead of you - whether they then choose to pass this information on is up to them.
In short: I couldn't find a reliable license provider offering decent support that charges less than cPanel themselves.
