The 'standard' six wheel drive configuration does seem like the most reliable drivetrain I've seen, and it can be implemented easily too. A dead axle system with a kit-style frame layout works great! Three chains per side; transmission to back wheel, transmission to middle wheel, middle wheel to front wheel. Give each one a tensioner, and you're done. This is the most common way I've seen it done, and I haven't seen one suffer a catastrophic failure yet.
As for the 25/35 debate, I'm all for 35, mostly for the reason that it's easy to obtain and keep working. <almost> No precision necessary. I also don't mind having the extra weight in the drivetrain; if you design the rest of your robot properly then you can afford the heavy chains.
And for the record, team 125 wins the best drivetrain award for 2008. 34 comes in a close second.