Summer Wars is better than all of them.
I have a love-hate relationship with Ghibli films, and even when I love them I'm often just lukewarm about them; I've never been particularly blown away or moved by them, and whilst the signature art style has grown on me, it's not something I'd really hold up as the pinnacle of animation.
I didn't really get what the fuss was about with Spirited Away - although I did watch that quite early on when I was just getting into anime, and I was more taken with Nausicaa and Howl's Moving Castle - and some of the later films (Ponyo, The Wind Rises) are pretty dire. When Marnie Was There was much better the second time I watched it though, and Arietty shocked me for being pretty good, even though I've despised everything Borrowers-related that I've ever seen before.
Hit-and-miss, but never enough either way for me to say it's outright terrible (just boring, mostly) or that it's one of the best things I've ever seen. I often feel like I'm watching an incomplete story that omits several key points and is over before it really begins; I have literally never been satisfied with the ending to a Ghibli film.