If you want a reliable existing platform, go AE. They're obviously the biggest, most successful name out there.
Look at the features. Although I switched, I don't feel that the Durango is a bad car. Bad cars don't make world events, even if they don't win it. Decide what you want out of this. Parts support or local expertise? Check your local track. New features and ideas? Then, think about Serpent.
If you do go with Serpent, you'll need some tools that you may not already have:
5mm Nut Driver:
http://www.amainhobbies.com/product_...Nut-Driver-5mm
4.5 mm Nut Driver
Not required but nice to have:
Serpent Ball Cup Tool:
http://www.amainhobbies.com/product_...-Ball-Cup-Tool
3mm Turnbuckle wrench:
http://www.amainhobbies.com/product_...nbuckle-Wrench