Better than the 1st one
For me, anyway. I know everyone likes the 1st one better, but for me it was kinda messy. The beginning was out of nowhere and not all characters were given a chance to stand out (Hawkeye and Natasha are most obvious examples). It was still great, of course.
AOU was better for me for several reasons. Every character mattered this time around (in extension to that, it felt a lot more as a character-driven movie than the 1st one.
Ultron was a better villain then Loki (again, imo), There's something about Spader's voice that is just horrible, scary, beautiful and unbelievable.
AOU has some pacing problems and, at times, unnecessary humor, but was more emotional than the 1st one also.
It's all personal taste and for me, this one betas the 1st one.