If you don't need data, then get the regular "talk" plan which is priced exatly the same as AT&T. 200, 450, and 900 minute plans available. AT&T only offers 450 and 900. Not sure which plan didn't fit your needs of not having "all the extra minutes."
The price differences come into play when you need data and texting. Unlimited texting on Sprint takes you to a $10/mo more plan. With AT&T, you have to buy a $20/mo texting add on service.
If you use data, and text a lot, Sprint is cheaper. If you just need talk time, no data, no texting, they are the same price.
Even with the $10 premium data charge, Sprint is still $25/mo cheaper than AT&T for my needs, which are 450 min, texting, and data.