Depends on what you want to do with the car. If you are looking for a well balanced driver then the 340 is the way to go. If your goal is maximum straight line acceleration and really don't care about handling an road manners the 440 is the way to go.
Also, the 340 swap will be a straight bolt in in place of the 318 and working quickly can likely happen in a day. The 440 will be much more involved and will require more work.
The other thing to consider, at $3900 you should be able to pick up a mopar crate 360/390HP, this will be a significant increase in power over a stock 340 rebuild and would be very close to a stock rebuild of a 440.
