You have a couple options
If you go with the s14 its going to handle better and your not going to have to worry about suspension for now. But, its a damn spendy engine and you dont have much options for power addons, Dont expect more and 270 at the crank easily.
If you go with the m50 its going to end up being cheaper, but your going to have some weight issues. The 318s suspension will not cut it for a heavy 6 cyl so your going to have to throw down for some new beefier stuff, which isnt a bad idea anyways and im sure eventually its going to end up on your "to-do" list too. And with the m50 parts a a dime a dozen and you wont have to spend near as much as you would on a s14 to maintain it.
If you hear what people say after swapping the m50, most wish they could have gone s50. Its the same swap just a bit more expensive engine, but you go from 189hp to 240. And the s50 has more aftermarket parts.
And, If you have a lot of money to burn, just head for the s52.
Where in MN are you? Im in rochester and I have a buddy in winona who sold me my s52 and could probably hook you up with an engine so you wont have to pay mad shipping on it.
Im turning into a swap guru after my e30 m3 s52 project, hit me up on AIM "eggbaker21" if you have any questions