I've got the SMC7904BRA and it rocks but I've never used the Billion - I guess the trick is finding someone who's used both otherwise their opinion will be as useless as mine
I have the Billion 7300G. This is a very reliable router that also supports half bridge mode from what I remember. The only negative aspect regarding Billion routers in general is that there does not appear to be a lot of software support for them from the user community i.e. there do not appear to be versions of software like OpenWRT or DMT for Billion routers etc. If you have a good line quality then Billion routers will perform very well but if your line is noisy and you are struggling to get 4Mbps speeds then it may be better to look at a Broadcom based model.
The Netgear DG834GT (the *GT* version not the G version which uses the TI AR7 chipset) is a very flexible router that can be used on noisy lines and has the capability to modify the settings on the DSLAM such as the downstream and upstream Tx powers etc. This router is very popular amongst the hacker community and different firmwares have been released to improve the features and performance in a number of areas. Alternatively the Thomson SpeedTouch range of routers are considered to offer the best performance on really poor lines. These models aren't available in SA but you can buy a refurbished one in the UK for around 20 Pounds (see the link). Look around on Google if you want more information about the best routers for noisy lines.