Seraphon or idoneth?

I am being interested in starting an army. I originally (couple of years ago) wanted to start seraphon so I bought a 2 start collecting seraphon and a celestial stampede box.

Looking at ebay prices I could maybe sell them for 330e.

Should I rather do this and get an Idoneth army (i am really drawn to them), or should I just buy some seraphon models and have the seraphon army (which I also like). If so, what would you advise to buy?