Since Zynga launched FarmVille on the iPhone last week, we’ve been watching to see how it’s received. The verdict so far: pretty well, although the game is by no means making a total sweep of the rankings. FarmVille has consistently held the number two spot in the free game rankings each time we’ve looked, after Rollercoaster Extreme, and is number four among all free apps.

A more interesting view comes through Apple’s listings of top in-game purchases. The two most common purchases are the two cheapest, with the premium currency, Farm Cash, being the preferential pick. But the most expensive option, for 310 Farm Cash, comes in relatively high on the list. Here’s how it compares to another farming-style game on the iPhone, Ngmoco’s We Rule:

Players have spurned FarmVille’s mid-priced Farm Cash offering entirely, leaving it at the bottom of the list, while $49.99 of Farm Cash comes in above a number of cheaper options in coins. We Rule, with its simpler structure of only offering one currency for purchase, also shows the habit of players to skip to the most expensive option. It’s also worth noting that, since we started watching, the most expensive option for regular currency, 70,600 coins, has risen significantly in popularity.

We’ll be digging into some stats from our latest Inside Virtual Goods report tomorrow, showing more in-depth breakdowns of heavy-spending users in social games, so stay tuned.