>>5646953First Edition Voyager Bulkhead or Prime are great. The PRID Vehicon is also cool. Some of the generations stuff was suggested like Springer/Sandstorm. Combiner wars isn't the best time to hop into an official line given how much of a step down the bots are, but headmasters are back next year.
You can also go unofficial and third party, but they tend to be expensive. Their are some god tier KOs like Wei Jang's tweaked and upsized evasion movie prime. Right now tiny pocket sized are the current hotness.
Also Machine Robo is coming back with a line of unconventional transforming robots. They're almost about to drop and aren't too expensive.
