In 2009, I picked up a copy of the 2007 film on a whim in HMV. I figured if it wasn't any good, at least there were robots to enjoy. I watched it that night and was instantly entranced - especially with Ironhide, who most people know as being my most favourite Autobutt of all time. (I cried in the cinema during Dark of the Moon. And then I raged.) The next day I was talking to Brent (@Brentosaur) over Skype and mentioned that I had watched the film, and he gave me a brief rundown of the Transformers franchise. But after that conversation, I didn't think any more about it...
...Until I went to GAME about two months later and saw the 1986 Transformers film on sale for the PSP. I'd only just bought the console and was looking to build up my UMD library, so again I picked the film up on a whim, and again I watched it that night whilst chatting to Brent. And I was hooked. I loved the animation, the cheesiness, and the designs of the Cybertronians. I loved Megatron's snark to Starscream. Hell, I even loved Wheelie. (Wheelie is a sweetie-pie who must be defended at all costs, and yes, I will fight you over it and I will own that third party toy one day damnit.) The next day I went to Sainsburys and bought a Voyager Class Desert Tracker Ratchet from ROTF. And that was the beginning of the end.
It's been six years and whilst I'm currently downsizing my collection to move out of my parents' house, I'm still keeping a good 150 bots. I think it's safe to say that I'm never leaving this fandom, especially with Hasbro giving it so good at the moment. Generations Arcee, man. One of the best toys ever made.
For the toys...ehhhh. You're looking at thirty years' worth! The G1 toys are solid but hard to find at a good price with all their parts, and the engineering won't be impressive by modern standards. The toyline from Revenge of the Fallen are the most tricky, and may be frustrating to beginners - especially the infamous Leader Class Optimus Prime. Really, the Classics/Universe/RTS/Generations/whatever the hell we're calling them now are your safest bet, especially the Generations line. And I still think Transformers: Animated toys like Lockdown and Blurr are some of the best ever engineered.
But really, I guess it comes down to whether the person is just interested in the toys, or the fiction. If you want characters you like from the comics/films/cartoons, then you're gonna go for those.
As for the franchise, I've sort of fallen out of the fiction lately - Prime did nothing for me and whilst I like the RID toys the show is kinda meh, and I've never been a fan of the comics because I like the sillier aspects of the Transformers universe. But I'm still loving the toys and the excitement they create, and that's all that matters for me. :-)