I need one of pic controller in little bit cheap also and can worth it. So i think medium pin count will be best. So from 28-pin pic controller's with USB which PIC is best. In terms of cost and RAM, ROM.

 

um... you look up the numbers, copy them to spreadsheet, then stare at them until you decide.

 

I also find choosing chips by pin count to be the best way of selecting and 18F2455 is BEST without a doubt. I don't know why they bother making all the others.

 

A quick peek at the Microchip Advanced Part Selector yeilds 183 MCHP parts found with 28 leads.
You are on your own to parse the list for cost vs memory.
(The PIC18F2455 is a bit long in the tooth these days, newer better cheaper devices abound.)

 

I was, of course, teasing ...

 

I was, of course, teasing ...

As much as I love sarcasm it does not translate well to the interwebs. A smiley face or such can help to indicate the intent but such subtleties oft get lost in translation, even more so when speaking to a non-native speaker of English.

And besides, what’s wrong with basing a selection on package size? Some of my best work was done inside very small package constraints. One was a micro and 60dB gain amp (at 3MHz no less) that fit on a board the size of a postage stamp. Another was a PWM controlled LED running off 10-28 VDC (either polarity) that needed to fit inside the metal band of a pencil eraser, and that included the LED too.

These both started with picking a package size for the micro.

 

Thanks ErnieM for giving suggestion of MCHP tool.

 

I think you should go with 18f2550 it will be easily available in market.