I found it good practice to have a reset switch on the board so whenever possible I use MCLR=on and pull up with external resistor + reset sw to gnd ... I only disable MCLR when I really need the extra pin. The pull up resistor do not take too much space on the board nor add some significant value to the price... If you are not going to use mclr as input, use it for reset.
If you decide to turn off mclr and use it as input pin, make sure that
- you have programmer with vpp before vdd option (any ICD like pickit2, junebug will work)
- you properly isolate the ICSP connector from the rest of the circuit