Dear Vexed,
To give some contrast to JJ's description, I've lived in the Wen Lin Jie area for about 3 years.
I'm not really part of the young crowd, but more of the middle-aged working crowd. However, I have been a Chinese language student for more than a year.
Pros of Wen Lin Jie: I'm partial to the food here. Western Cafes abound (Salvadore's, Mazagran, French Cafe, Vintage, etc.) along with Italian, Indian, Japanese, Korean, and Thai. Plenty of Chinese food as well. However, after a year, the scene can get a bit tiresome, but I think that's the case for most places, not just Wen Lin Jie.
For shopping, there's a Walmart about 20 minutes walk away, you can take a short ride to Carrefour, and there are local stores to fill some shopping needs and Paul's Shop/Green Kunming to fill slightly more expensive Western needs. There's bookstores, candy stores, clothing stores, shoe stores, etc. all around, but as a foreigner, you may or may not find this accessible (depends on your taste and size).
For convenience, many people come to this area to meet and drink so it's a great place to live if you want to meet friends for dinner or a drink. JJ's Toast Master's is just nearby on 121 Street; there's ping-pong tables and basketball, badminton courts nearby, and the green lake is literally at your door step (a really nice public park).
The Cons: The rent is more expensive here and apartments are older. The further you get away from Wen Lin Jie and the Green Lake, the cheaper prices are, but then, the less convenient the location. As a student, I ended up only getting to know Wen Lin Jie my first year (mostly) and got stuck in a routine of visiting the cafes, hanging out with foreigners, and basically not interacting with Chinese locals. The Kunming expat community is smaller than you think, so, for better or worse, you'll start seeing the same faces after a time. Wen Lin Jie is much louder than up north and the crowd here is younger, mostly students or travelers, and change every few months.
That's all I can think of for now. It might come down to why you are coming and how long you are planning to stay. If you plan to work in the future, you may want to think about being close to your future work (though you probably wouldn't know that right now) or if you plan to stay long term, then the north may be better for settling roots. Just my two jiao...Steve