The model numbers are confusing, because some are exclusive to particular retailers. It's a headache to try to keep all the configurations straight. The easiest approach with Asus laptops, IMO, is to figure out which components can vary in the given model you're considering. In the G74, that includes:
- CPU speed: 2.0 or 2.3GHz
- RAM: 8-16Gb
- HDD/SSD configuration: many options
- Optical drive: CD/DVD combo drive or CD/DVD/BD drive or BD writer drive
- DIsplay: Full HD or HD+
- GPU bandwidth: 192bit or 128bit
- VRAM: 1.5Gb or 2Gb or 3Gb
- WLAN card: WLAN+BT combo card or WLAN+WIMAX combo card
Decide which options are important to you, and then just look for any configuration that comes closest to your desired specs. There are some components that are very easily & cheaply upgraded after the fact (RAM, WLAN card), so I wouldn't let those be deal-breakers. Even the HDDs and ODD are pretty easily changed later.
Beyond that, choose a retailer that has a good return policy...i.e., no-questions-asked returns accepted within 15-30 days. If you have any of the known hardware issues, like a bad keyboard or touchpad, you want to be able to just return that unit and get a new one.
(Note also that Asus laptops purchased through certain retailers, like Best Buy and Staples, are not eligible for Asus' extra warranty features.)