It's not a question that's easy to answer but that everyone has an opinion about. These opinions can be split up into two basic camps:
1. Readers like shorter chapters, because they lack attention span.
2. Readers like long chapters, because they make assumptions about shorter chapters being badly written. (I used to make this assumption because short chapters on fanfiction sites are usually just baaaad, but I've discovered in the world of original fiction that's not true).
The irony is both of these are true. They are just talking about different groups of readers.
There's a few possible ways of dealing with this and all are equally valid.
1. Figure out which camp you are part of and write to those lengths - what you prefer to read is probably your target demographic.
2. Find the sweet spot that appeals to both. Updates somewhere between 1k and 1.5k tend to be short enough for most of group 1 not to lose interest but long enough to placate group 2.
3. Split longer chapters up into more managable chunks (and make it clear they are sub-chapters).
4. Just do whatever you feel like. Pick a length that won't burn you out and go with that.
There are successful serials at both end of the installment length spectrum so I think it's actually less important than people think. My serials have different installment length:
Dragon Wars (well strictly the side story Caredale at the moment): 500-1500 words an installment tending towards the lower end of that spectrum because I need a new desk and writing on my lap is harder for some reason. I wrrite much more when I sit at a desk.)
Haventon (currently sporadic due to writers block but around 2k an installment when posted)
Whisper (about 1k an installment but also blocked at moment)
Tales of the First (This is an experiment. I'm updating it daily by about one mass market paperback page (250-300 words), and the actual chapters are 4-5k long. I have shedloads of buffer on this but need to get working on chapter five so I can maintain the pace).