On 18F and higher it is pure masochism to use assembly language. With so much possibilities to scr** up. Assembly comes in play only as part of very time critical pieces of program, all the rest is better to be written in an higher programming language, C, Pascal even Basic.
Your assembly code will never be optimized as the compilers do the optimization (except you are top notch programmer who wrote the compiler).
If a piece of software takes 1 day to be written in C and debugged, it may take you 10 days for same effort in assembly.
In PIC18 you have more resources, more Flash, more RAM price almost the same, even cheaper than PIC16F, use C compiler and save yourself of headaches.