Unless you're pressed for space, it may be worth considering dedicated separates. Many companies tend to excel at one aspect e.g. the printer will be good but the scanner leaves something to be desired. Combined machines are more complex too, and you may lose functionality in all area if one goes down.
FWIW I use Canon printers because of refill costs, a software fax programme and a Canon scanner based on the reviews (don't use it much, though)
I realise it's not what you may want to hear, but perhaps worth looking into.
If you do decide to combine, ensure you know where you'll be going for maintenance and approx costs for the most common jobs before you buy!!