Welcome to flyertalk! I own the original Platinum Magna 25 and several other items in that line. I also own a number of Eagle Creek accessories, not suitcases.
First, I would definitely NOT get any suitcase larger than a 25-inch size. I took that size plus a carry-on size backpack on a 5-weeks trip all over Europe a couple of years ago. I had problems getting OFF trains with those two pieces, in fact I literally fell to the platform exiting the train in Warsaw. The weight of the 25-inch bag plus backpack caused me to lose my balance. Train steps to the platform are high and difficult to navigate with luggage, at least they were for me. I vowed that I wouldn't take anything but carry-on in the future on trips to Europe.
That being said, if you really must travel with a checked bag I definitely recommend the Platinum Magna line. I've checked both the 25- and 21-inch bags multiple times and they came through with no marks. My PM bags are spinners, which I prefer, and the 25-inch was easy to handle even on long walks to hotels. I visited Istanbul, Krakow, Warsaw, Berlin, Paris, and a few other cities on that trip. No problems with the spinner.
That being said, I'm making another solo 5-weeks trip in September to Bordeaux, villages in southwestern France, Carcassonne, and Barcelona. This time I'm determined to take carry-on only. I purchased an inexpensive Travelpro Maxlite 4 rollaboard (2 wheels) and a Pacsafe super-secure 25L backpack for this trip. I figure I'll be navigating more cobbled streets this time and 2 wheels will be more sturdy over uneven pavement. With the 22-inch rollaboard and smaller backpack, there will be no more falling off trains for me!
IMO, you can't go wrong with either the Platinum Magna or the Eagle Creek bags you've mentioned, but don't go over 25 inches! If you'll be walking distances to hotels you would want to consider two wheels rather than a spinner, although I much prefer a spinner if walking on sidewalks and paved streets. I looked at several Eagle Creek bags for my upcoming trip, but decided on the less expensive Maxlite 4 since it won't be checked at all. Also, keep in mind that 2-wheel bags hold more than spinners of the same size.
One other brand you should consider would be Briggs and Riley Transcend, the line is currently on closeout so you should be able to find bags at a discount. (Not the new Transcend VX which has just been introduced.) B & R has a great warranty and the Transcend line is sturdy and attractive.
No doubt others will chime in. Lots of luggage geeks frequent this forum, but many of them prefer higher end brands like Tumi and Rimowa. I think you're on the right track with your brand choices.