The only reasons to use the older 14bit or 12bit cores are 8 & 6 pin packages and ever so slightly cheaper than the 16bit core.
The 18F have free Student editions of C (C18) and BASIC (Swordfish), more options (USB, Ethernet), more RAM, FLASH. Improved instruction set with none of the oddities of a MPU designed in 1977 (the original PIC1650) on which the 16 series were based.
IMO a PICkit2 / 3, Swordfish / C18 and an 18F is as easy to learn and offers more flexibility the very popular Arduino.