Sorry hope this is ok, not a code question but you smart guys can tell me...

[HenrikOlsson]

Hi,
It's really only you who knows what you want to do and you can compare the features of each device to see if they have anything that you may want to play with.

The 16LF84 is a VERY old device, can't see why you or anyone else would want to use that for anything new today.
The 16f877a is rather old as well but does the job, don't think I'd pick it for a new design though.
The 16F777 seems to be pretty identical to the 16F877 but with the added internal oscillator block and power saving features.
The 18F4320 doesn't seem to have any features that "pops out" so to speak. It seems to be the 18F series equivalent of the 16F877.
The 18F4455 is exactly the same as your 4550 but with LESS program memory (24k instead of 32k).

The 12F675 and 12F683 are both cool little devices that can come in handy.
The 18F4580 has a built in ECAN module so if you see yourself playing with CAN networks then that might be good.

Overall, all of the above devices are rather old. There's nothing wrong with that but there are newer and cheaper alternatives.
The 18F46K22 for example, lets compare that to the 18F4320 above. It has the same amount of I/O (well, one less actually), 8 times the amount of program memory, 7 times the amount of RAM 4 times the amount of EEPROM, 60% higher clock frequency, internal oscillator, broader operating voltage, more analog channels for the ADC, the list goes on - yet it cost less than half of the 18F4320.

I've been kind of stockpiling chips over the years. When ever I'm doing a new project there are a new better, cheaper, cooler device available that I want to use instead of the old, kind of boring pile of chips. The only one I haven't been able to "updgrade" is the 18F2441 but I hope they come out with an alternative for that one too.

/Henrik.