I played Frontier but I haven't finished it and right now I'm playing ToD.For me I like ToD better because I like the new farming system where my monster will take care of my crops and I like the fact that we get a scene as we befriend the villagers.About the character both games have interesting characters.ToD battle system is better than Frontier.So I recommend ToD but if you want to play Frontier it's also okay because both are good games.Maybe you can check a video or two and see which suits you better.
Now Playing : Rune Factory ToD Going to play : Tales of Xillia
Is RF3 an option? It's the one I got hooked on to the series with. Best and closest to HM style, IMO.
Frontier is next on my list, but I really enjoyed ToD. I would recommend that if you REALLY love the farming/dating aspect, then go with Frontier, but if you like/love dungeon crawling, ToD is your better bet. I say this only because of what I've heard of the runey system in Frontier- if you'd enjoy the system, then the game would be fine to start; if you didn't, it might turn you off of the series. ToD's farming system is almost nonexistent, and even though I've beaten the game, I think I only actually focused on farming for one game day in the 1.25 game years I played.
If you really liked the Harvest Moon series, then I suggest playing Frontier first (or, as suggested above, Rune Factory 3 if you've got a DS) since it's got a more traditional farming system. Then, if you like Frontier, you can go onto Tides of Destiny (which simplifies the farming quite a lot).
A small tip for Frontier, you can plant ANY crop in the whale island dungeon and it will grow. The other 3 dungeons have a specific season tied to them. There are some flowers that you can only grow in a dungeon because they can take 40-120 days to grow.
Masamune456 posted... Thanks guys I picked up frontier as I really really enjoy the farming aspect. Really fun so Far!
Just make sure you don't ignore the Runey system. It needs looking after from the very beginning. A lot of people seem to just ignore it (or sometimes even somehow fail to realise it is there) for ages, and then they wonder why all of their crops are dying.