Well for cheap and easy bolt in you can go with a 1.9L HO out of a escort GT 89 and lower or go with a 2.0 SPI out of a 97-2002 escort. Both will bolt right in with very little modification. If you want to go a little more extreme you can go with the mazda based 1.8 out of 2nd gen escort GTs. As for the B6T they are very hard to come by as they where put in the 323 GTX 4wd models. Good engines but for ease of location and price it's a good bet you'll have your work cut out for you.
On the other hand the KLZE 2.5L V6 is a pretty common swap that is do-able but requires alot of modification
the F2T 2.2L turbo is a great engine but good luck finding one in good running order.
as for rotary engines, unless you really plan on dumping alot of money into your car its a waste of time.
I've owned a few 1st and 2nd gen RX-7's and although they are great engines, the amount of work involved to put in a rotary is alot. the 12A and 13B engines are a better route to go if you plan on converting it to rear wheel drive. The 12A is a great engine and pretty dang strong. the 13A is a waste, go with the 13B. You can take your pick of a 4 port or 6 port 13B turbo or non. If you plan on going teh 6 port 13B turbo go with 88-90
Either way you go, make sure you have done all your research before you start getting the parts.
Good luck