I have gathered crops information from various web sites and on my own farm to determine which crop is best to grow. There are many worksheet out there with information but none is complete and up-to-date. I have combined them all into this one here. I also have updated it with new crops including avocado, pomegranate, broccoli, and starfruit. There are a few missing fields still but I will update them as soon as I get the information. If you see anything that needs update, please let me know.
As you can see from the data, besides the love flowers, all the new crops have very high profit margin if you can grow them. They all require level 30 and up.
Below level 30, Mistletoe has highest profit margin and only requires level 25. Grow a lot of mistletoe if you need money quickly. Next up would be the secret datura requiring only level 20. They produce pretty hefty profit as well.
Below level 20, grow cashew (level 17) though I have found that cashew tools are hard to come by for me. Pistachio is another crop that falls into this category. It is fast to grow, make lots of profit, but hard to find tool for.
Anyway, you get the idea. Just go down the list and see what crop is best for you at the level you are on.
List updated on June 1, 2012.