I've used both, although you'll find the hc705c8 is obsolete. However, Freescale have the hc08 series which is quite a good series - a bit quicker than the hc05 series. As I've mentioned at other times, the architecture differences are hidden for the most part when you use 'c'. I try to make it a point of only writing in 'c' unless there is a customer request or economic consideration that I use assembler.

Freescale make available a free limited code size 'c' compiler for most of their parts which is worth a look. I used this and a 68HC908QY4 part recently simply to replace a handful of discrete logic. I didn't even have to look at the cpu architecture! This connected to a 8051 based unit, again all written in 'c'.

Generally, for people who write in assembler, they don't like changing architectures. After a while you get to 'think' in a particular architecture. I had to write an app in PIC assembler recently - that took me a bit more time than I had anticipated. I had to learn another IDE (MPLAB) and cope with the quirkiness of the PIC architecture - many things are not done in the 'obvious' way in the PIC, so you have to learn these and the PIC is real quirky. Interrupts for one are really crude and table lookups are 'interesting'. However, you have to admire how those small handful of instructions can be coaxed into doing things - albeit not that obvious.

How would rewriting the logic analyser on a 8051 change anything? Would it work better? Most likely it would do the same thing, just the name on the cpu would change. In short, a micros do much the same thing, each has its advantages/disadvantages - in many applications you could choose from over a dozen parts that would all work - it really comes down to what the engineer knows and what tools are available. As such there is no 'best' in many situations.