I think the Spectrum was more *interesting*, even though the C64 was technically better. After all, the Speccy had Your Sinclair in its corner; it had the Rochdale Balrog, it had Ultimate, it had Chaos, it had Sweevo, it had Tir Na Nog. It spawned - with later ports - Lords of Midnight, Jet Set Willy and Tau Ceti.
I think the Spectrum is where I got my love of the breadth and variety of gaming - and from the outside looking in, I don't quite see where I'd have got the exposure to that if I'd had the C64. I will happily concede that that's an attitude born of ignorance (and indeed, given my fondness for text adventures I'd love to get an idea of what the independent text adventure scene on the C64 was like, because that's a massive blind spot in my understanding of the history)