27/17, 28/18 big barrels

I use Justbats.com
Their prices are competitive and they ship immediately. The bat usually shows up within a couple days using standard or free shipping.

I'm cheap. So, I usually just buy last year's Easton Stealth or another popular bat from a previous year that has a proven track record and is greatly discounted. My son likes the carbon handle look and bright colors on these bats. I don't spend much on them relative to what his teammates spend. (I'm old school and I don't think great hitting is a result of the bat as much as it is a result of the batter. Put it this way, Lance Armstrong is still the greatest cyclist whether he's on a $100 Huffy or weather he's on a $7,000 Trek. "It ain't about the bike.")

One word of caution about purchasing on-line versus using your local dealer. Our team has had a rash of defective or under engineered bats come through in the last couple years. We've had Catalyst bats crack and break in just one or two games. We've had several Prodigy bats dent with minimal use, etc. Fortunately, those bats were purchased via a local dealer. The bat companies warrantied out the defective bats with no questions asked. Generally, dealing with warranty issue via internet sales sites is a pain.
BTW, we are still using Prodigy and Catalyst bats on our team. The warranty replacements addressed the defects from the original bats. And I use older model bats, like the Easton Stealth, that are proven to be durable and on sale from 2006 or 2007.

TPX Omaha's are good bats at reasonable prices.

My son has outgrown his 27-17 TPX Omaha, but smaller kids on the team use it, and it has done great. His 29-19 Catalyst has been very good, and his 29-19 Prodigy has good pop, but it's square (I kid you not), and he has only been using it for less than 2 months. We always buy our bats from JustBats and are very happy with their service. They actually replaced my son's first Prodigy when it dented the first game, but now we have to go through Worth to replace the current one, and Worth hasn't been so helpful. (Kinda tough to return a bat and have to wait 2-3 weeks in the middle of the season). We are thinking of just getting him a Demarini Vexxum as his main bat, and just selling the Prodigy replacement when it comes in. We've heard many good things about the Vexxum.