What to do...

The same story as always= How much do you want to spend?? I have had and done them all from 170 to 472 cubic inches and had a love/hate relationship with them all.
Take a 225 and throw about $2,000 at it and you may get it to run mid to high 15's depending on what car you are putting it in.
Take a 318/360 and throw about $1200 at it and run low 15's to mid 14's again depending on the body.
Now you can go with used parts/do barter/swap and do better.
There is nothing like the feeling when some one comes over to you after you chase a group of cars(Hot Rod Power Tour) at 115 mph+ and you hang on to the back bumper of a Chevy or a Ford (or another Mopar for that matter) and they ask you to open the hood of your Dart and find a Slant 6. The guy in the Chevy just said "Please don't tell anyone,I tried my best to shake you damn it"........Priceless
It would have felt good if it had a 318 too but I don't think he would have been as embarrassed.
So price it out and see the best way to roll. Have fun and good luck !!