Just my 2 cents on this topic. Please kindly flame me if you think my opinion is wrong.
Intel:
Everyone recommends Intel NICs(just Google). They are rock stable and won't crash even under the most heaviest loads. There's a reason why they cost a whole lot more than other brands and that's because Intel hardware design is top notch and they have one of the best software documentation and support in the industry. Driver can be extensively tuned either for performance or reduce cpu usage or balance of both. In a nutshell you won't go wrong with Intel.
Realtek:
Back in the days of Windows XP/Vista, PCI based Realtek 10/100 controllers were "notorious" for all sorts of network connectivity issues like slow speed, random disconnects or web site not loading. Operating System included drivers if not updated to latest version usually resulted in very poor performance. Flow control and Auto Negotiation often caused alot of performance issues.
However, modern day PCI-E Realtek 1GBe Controllers integrated into most consumer grade systems are actually very good and stable for most home/SOHO usage. They are just as fast as Intel or other brands in terms of throughput and all features like TOE and Checksum offloading are working fine for most usage. However their driver feature set, open-source operating support/features and documentation isn't as good as Intel. If you plan on running a system for mission critical, the general internet opinion is: Don't use Realtek.
Atheros Killer NIC:
What's the point of having a NIC that has increased CPU utilization?
Broadcom NIC:
They are generally fine for normal use, however TOE can cause NIC to stop functioning under very heavy connection load.