I think if it's a matter of saving $20-30 (which is likely how much cheaper it may be found elsewhere), I think it's always the best bet to go with a Verizon store. However, I have read that Best Buy offers their replacement plans, which is more expensive up front than the standard insurance, but cheaper overall, and much more hassle free when it comes to dealing with any issues.
Also, I would stay away from Wal-Mart if they are upping the price for the secondary line. My wife and I are on a family plan (her line is technically the primary line) and we got her Eris for free with my Droid ($199.99).
I think overall just consider what type of customer service you prefer. You will most likely be able to find the cheapest prices online, but you will have no face to go to if you have questions or run into issues. In the store you can tinker with the phones, ask all the questions you want, and you will always have a place to return to with any future issues.
