USB to ethernet adapter

[Wesley M.]

Hi, 

I'm going to build a small firewall with proxy cache for web.
Using an Apple Mac mini. For the second ethernet, i will use :
- Trendnet TU2-ETG OR Apple MC704ZM.
What is better ? using trendnet or Apple Adapter ?
And is it enough stable to use a USB Adapter ? 
Thank you very much for your answers. 

Wesley.