This has been discussed so many times.
i bought viewsonic g tablet but returned it for an archos 101 because of very bad viewing angles, however archos 101 viewing angles are not that great too but somewhat better then g tablet.With g tablet you have the options of custom Roms which is a big plus, where as archos is more lighter but strictly locked down to stock rom.
On paper specs of g- tablet which is tegra 2 powered certainly beats down archos.
What you mainly want to do with your device?. If you want to play lot of 3d games or hacking then choose G tablet , if you want to play videos, light surfing and checking email, choose archos 101.
my original motivatiion was just to conduct business( pring and compose word docs etc.) and read .pdf files. but when i started to dable in the world of tablets i read about battery life and upgradeable OS' and decided i had better make a wise choice. Now my main interests are video chat and the ability to run honeycomb since my main needs will be covered. I do like the archos better but some say the veiwsonic is a better built machine
Both can display pdf files or word processing with right apps, but G tablet is certainly more powerful and also got a chance to update to honeycomb in near future.I use my lightweight archos (with working market hack ) for light browsing,checking emails,and to play games Archos serves my needs well and im happy with it.but i might upgrade to galaxy tab 10 or asus ee transformer in future.
I had an Archos 70 and while I did like it the battery life was terrible and the touchscreen was laggy at times. I have the Gtablet now and I feel like I definitely made the right choice. The viewing angles really aren't that bad and the responsiveness of the gtablet is light years ahead of the Archos.