Ah, we haven't had a "best brand" question around here for,,,let's see,,,at least two days:-(
Do you have a budget, or is the sky the limit?!
You can get all kinds of random responses, but most will be meaningless without a specified budget.
Oh, brand is usually immaterial. As you go to higher level road bikes, the component groups are higher quality/performance. This is reflected in the price.
Edit: $600 is limiting, but not the end all. For new bikes, consider:
1. Jamis Ventura Sport
>>about as inexpensive as you'll find in a quality, credible road bike with STI shifting.
2. Kona Honky Tonk
>>this is a cool bike that features downtube shifters to keep the cost down, but the quality is excellent for the money.
3. Order a Mercier, Fuji, Dawes or Windsor from bikesdirect.com. In your budget, you can select from a variety of models with different options. The downside is you'll have no help with sizing or adjustments, and you have to do the final assembly and adjustments,,,,or pay someone to do it. Still a very good value.
4. Toughen up and go with a singlespeed. Okay, I'm having some fun here, but a singlespeed may be an option for you if you don't have many hills around. Bikesdirect.com has several. There are also the Kona Paddy Wagon, Jamis Beatnik, Raleigh One Way, and Trek Soho among others. Not paying for shifters and derailleurs can save you money if you don't need it.
Good luck, ride safe, and Live Strong (j/k)