It really depends on what you're looking for and what your tastes are. Since you were inspired by TFOne, Transformers Prime is probably a good starting point. The original 1984 series Transformers (also known as Generation 1) is not bad, but is definitely a product of its time.

Beast Wars can be watched without prior knowledge, and it's great, but some people can't accept early 3D graphics. Car Robots is a more comedic take; Transformers Animated is a very well written and loved series; Cyberverse is generally good, but it takes a while to really get going.