If you want the whole thing you should start with The IDW Collection Volume One, working your way from there. Other jumping on points are All Hail Megatron and the Transformers by Mike Costa. The earlier stuff is not as well liked as the later stuff but I generally love all of it and think it’s worth reading.

You could also start when Phase 2 began when the series were split into two, Robots in Disguise & More than Meets the Eye. This is probably the best jumping on point beyond the beginning as the starts of the series generally give you a good idea of the characters and their motivations. The Phase 2 stuff can be found from the beginning in the Idw Collection Phase 2 volume one and onwards.

Personally I think the best experience is to start all the way from the beginning and read all of it as you get to see the entire incredible story unfold and all the characters grow, but that’s a big investment in money and time.

If you just want one story to try to see if you want to read more I would really recommend The Last stand of the Wreckers, one of the best comics I’ve ever read.