The M20 stroker will plop in and bolt right up a lot of work is needed to make the M50 motor and trans not only bolt in but run. A complete M50 engine wiring harness is needed and about 25 man hours are needed to do the install, and that is if you have everything there sitting. To build a M20 stroker it'll cost about 1200 if you do most of the work yourself. To even buy an M50 motor and trans you are looking at 2000-2700. Plus for you to make it smog legal you'll have to buy new cats since it is illegal to buy used cats then you have the exhaust to contend with. A stock M20 2.7 puts out 120HP and 170 ft-lb a well built stroker has potential to equal that of a M50 motor which makes 192HP and 181 ft-lb of torque.
In the end it'll be a labor of love because you'll never sell the car for enough money to recover half of the total (motor labor parts etc.) Is it worth it? I hear that the M50 motor really turns the e30 into a new car and they swear it's worth every penny. Where others have said it was a nightmare and regret ever getting into it. Do some research, there are several sites that cover the swap step by step, take a look at what is involved and see if it’s within your skill level and affordability.
Honestly if your car is in exceptional condition inside and out, a #1 or #2, I'd say do it, but if your car doesn't look good from 100' well I think I'd spend the money on the car...