Luggage Carry Overnight

Travelling europe for 8 weeks, opinions, suggestions?

Hey all. Mid next year my sister and I are jet setting out of Australia and travelling parts of Europe for 2 months. We're going to be travelling to all different places over our 8 weeks including London, Italy, Portugal, Scotland, Ireland, Ibiza and a couple others. I want to know what you recommend to take as a travel bag? A suitcase, or a backpack? I will ofcourse be taking an overnight sized bag too for the plane etc., but I have had so many opinions as to whats best to take my main luggage in; a large suitcase, or a large backpackers backpack? I have never travelled overseas before so im not sure what is most convenient when it comes to wheeling a suitcase around or carrying it on your back while journeying on train rides, bus rides and even walking from place to place.. We will be staying in backpackers villages at times, but hotels other times. What are your thoughts? And do you have any other advice or suggestions for travelling europe?
Thanks heaps for your answers

Something with wheels that you can drag along, and with a secure lock. Backpacks are exhausting and only really designed for if you are climbing mountains without a decent footpath.

Check with your bank that you can use your ATM card in the machines here, and let them know your travel dates.

Get travel insurance.

Bring a Visa and/or Mastercard. Don't bother with any other credit card.

Check the weather for the season you'll be there, and bring appropriate clothes. And remember weight - airlines allocate a certain amount of weight to each passenger, you go over this, you pay extra. With this in mind, be prepared to post souvenirs home.

As regards Ireland, be prepared for any kind of weather. Seriously. I live in Ireland.