In my opinion you should stick to one type of instrument while you are carrying out your PPL and also one type of aircraft too. The basic idea of being a student pilot is to learn how to fly. This is hands on stick and rudder gradually teaching your mind and body how to deal with a totally unnatural environment from a human point of view. Any unnecessary distractions should be avoided. After this and with a shiny new PPL in your hand you can start moving on to other things like different aircraft, twin ratings and indeed different instrument systems. Many PPLs lapse after getting their licenses and this is because the challenge has evaporated. If you keep this alive by doing different things, the joy of flying will stay with you.