I'm at Marris and I absolutely love it! Really cheap (£96/week, currently £3,675k/year but might go up for 2016), toilet and shower only shared between three, pretty good location and a lovely kitchen area. Other than that, Park Terrace has seemed lovely when I've been for prinks, even though there aren't any pictures on the Newcastle Uni website (though don't know if it's reaaaaaaly worth paying extra for an ensuite), and people at Leazes Parade seem pretty happen. I would recommend avoiding the managed partnership ones (Liberty Plaza, The View, Vicky Halls etc), as they are further away from campus and the other uni accommodation, and usually not as sociable, and in my opinion it's not really worth nearly £2k extra/year for just your own ensuite. My friends in the managed partnerships ones really don't seem too happy in them.
If you have any Marris-specific questions then feel free to ask