I suggest you learn and use grammar first. Use capital letters and full stops, and only use question marks where you're asking a question. Don't try to type as you would speak in casual conversation. Also spell out words in full. Using txtspk mks u snd lk a teenage girl. and it's unnecessary if you've got a full keyboard in front of you.
The choice of register will depend on the functionality attached to that register. If you need to perform mathematical operations on a number and only A is available to the ALU then you should load A. If all registers are available to the ALU then the choice is down to whichever register is available.
Your CMP question made virtually no sense, the only thing I could deduce from it was that you're way out of your depth, and if you're on a course you should see your teacher and tell them you're completely baffled.
Finding the largest of a set of 10 numbers is dead easy. Work out how you might do it on paper first. Restrict yourself to the abilities of the microprocessor; don't just look along the list and say "that one". You'll need to tell it where to start looking, then you'll need two variables, one for the size of table and one for the maximum number found. Loop over the table looking at each value in turn and comparing it with the current maximum (for which you'll need to think up a suitable initial value). If the current maximum is less than the table entry, replace the current maximum with the value in the table.