Both routes are excellent walks. If you go from Lake McKenzie, following Explorer Creek, there is only one small hill just after walking around McKenzie, and after that, it's all pretty flat and easy. The track does peter out a bit just before Lake Explorer, but the navigation is not difficult if you're experienced at it.
If you're really into off-track walking, my preferred route would be to walk in to the Blue Peaks, then keep going to Little Throne Lake, then cross country and off track to Lake Halkyard then Lake Nameless, then out Explorer Creek (a great circuit, starting and finishing at Lake McKenzie). This way, there is very little in the way of hills, there is no covering the same ground twice at all, but you still start/finish in the same place (within a few hundred metres), you pass by dozens of top fishing lakes, and great scenery, you get to optionally climb TWO of the smallest and easiest mountains there are (Forty Lakes Peak, Little Throne).
In fact, if I was to do it, I would skip Lake Nameless altogether, and camp somewhere in between Lake Halkyard and Little Throne Lake. There's plenty of good camping right through that area.
Of course, all this assumes some good off-track navigation skills. Even when on track, the Blue Peaks track is poorly marked in some places and easy to lose. The landscape in some parts on that track is also devoid of significant land marks making navigation even more difficult, and to top it off, there's iron in the rocks which interferes with compasses. So you've been warned. If you're prepared for all of that, then this is one of the best circuits you can do anywhere with easy walking and lots of lakes.
PS. Links to trip reports on these two tracks which can be easily joined into a circuit with a bit of off-track navigation:
Blue Peaks TrackExplorer Creek Track