ha. This is a question I had many years ago. The 168 bulb is a brighter bulb because it is a higher wattage bulb than the 194. Both are the exact same size. You'll see all aftermarket bulbs on web sites show 194/168 wedge or some similar type.
Super Bright LEDs - Bulb Cross Reference
As far as which led bulb is best? Sorry, but there's really not much of a definitive answer. I've commented before that you'll have to research the brightness and angle of a single led then determine which bulb you want to buy. Some sites make ridiculous 194/168 type bulbs with 9 or more high intensity bulbs for retina searing brightness. More sites pop up every day selling single high-intensity bulbs to several leds. Here are my two preferred sites to get bulbs from:
SUPER BRIGHT LEDS home
www.autolumination.com Tail Light Brake Light Turn Signal LED Bulbs
You can also try these sites.
V-LEDS.COM High Power, SMT, Super Bright LEDs, HID Headlight Kits, Automotive Interior & Exterior LED Bulbs
Luxer1 PRODUCTS LED DOME LIGHT
My preference is the WLED-WHP single bright white bulb from superbrightleds.com. I use it in every location that uses a 194 bulb (bumpers, door, gauge cluster)