NCT - from Marilla Trailhead to Red Bridge access - is a fine stretch of trail, well blazed and well maintained (though there were occasional downed trees that needed to be cleared from the path). Connectors to the Manistee River Trail (including a really great suspension bridge crossing the river near the Hodenpyl Dam) allow for an ambitious loop day hike from Seaton Creek campground. The NCT climbs the tree-lined ridges along the Manistee River valley, pleasant, modestly challenging and sparsely traveled (it's a popular trail for really tough mountain bikers, but i only encountered one hiking family and no bikers). There's a short spur on the southern portion of this stretch, to the Red Hill Lookout - the views were mostly obstructed by foliage this time of year, but lots of wildflowers. All along the trail, the fauna is varied, and lots of critters (including birds of prey), too.
The Manistee River Trail, in contrast, hugs the river, is poorly blazed and poorly maintained, and throngs of beer drinking locals camp all along the banks - though the views of the river are spectacular in some spots. Overuse is taking a toll on this trail, but with a little care and upkeep it could be spectacular.
Unless you arrange for a pickup at Red Bridge (or similar access point), you should take the MRT as the second half of your loop, as the travel is much easier ... and it allows you to appreciate just how nice the North Country Trail is! It leaves me wishing for easier logistics in hiking other portions of the NCT, where transport back to the trail head is a must.
BTW, I was here last autumn, and its a PRIME time of year along these two trails!