I always felt like Girls Aloud were a great singles act but they don't have an album I'd consider a stone cold classic. Sugababes don't have multiple of those either, but Three is an excellent record and the Sugababes' classic sound hasn't aged.
above all Push the Button I think is the best song by either group and has aged incredibly well. almost all of Girls Aloud's music sounds more of its time because Xenomania had such a specific sound in the 00s. they probably did better work with Girls Aloud than they did with Sugababes. Mutya hates Red dress and Keisha can't stand Ace Reject (sad!). but they also produced Round Round which again I'd argue is as great a song as any Girls Aloud single.
it's super interesting that they both existed in parallel for long periods of the 00s, but never really felt like competition, even when sharing producers and songwriters. I think most of Sugababes' music was made on their own terms and most sounds of it fresher to me today. I don't think Girls Aloud could make new music now (not because Sarah is gone) but Sugababes can and are, and I have faith it will be great and reaffirm why they're still here in 2025.