The Europark looks like quite a nice hotel (far beyond my price range!), and the Eixample is a good area; not very touristy but with restaurants and handsome buildings. There are modernista buildings scattered around the Eixample, so if that architecture is one of the main things drawing you to Barcelona, the Eixample will be a good home base.
The Europark would also be quite convenient for visiting La Sagrada Familia, Casa Mila and the Picasso Museum. Parc Guell pretty much needs some form of transportation from just about anywhere you might stay (bus or taxi is best unless you want to walk a mile uphill). The Europark's location very near the Girona Metro station is a big plus for getting to other places for which transport might be needed (like Montjuic).
My question is: How many days are you going to spend in Barcelona? If it's a rather long visit and you are going to want to keep returning to the Barri Gotic/El Born/El Raval areas, you might prefer to be not quite so far beyond Placa Catalunya. But the closer-in areas can be noisier and certainly are far more touristy. It really depends on what you prioritize.
Edited to add: Barcelona has some fairly widely-scattered sights, so you should expect to occasionally need some form of transportation. However, I stayed there for 10 nights and went to several rarely visited modernista sites in obscure locations and still used only 6 of the 10 rides on my T-10. I am a big-time walker and was staying very near Placa Catalunya. I walked the 2 miles to Montjuic more than once, really enjoying the sights along the way.
