I have both a Luminox 3101 and Marathon Navigator. As far as performance, both run accurately as a quartz watch should, though I believe the Luminox has a higher jewel count Ronda movement (I read 5 jewels in a post over on TZ-UK) vs the basic 1 jewel ISA in the Marathon. I definitely prefer the overall look of the Marathon but since it is all plastic/composite I don't know how it will hold up versus my stainless Luminox. The bezel is definitely better on the Luminox, plus the design of the chapter ring may allow you to replace tritium tubes down the road. The Marathon will need a replacement dial since the tubes are attached directly.
I had my Luminox exactly one day and I scratched the "scratch resistant" mineral crystal. o| Duarte at NEWW replaced it with sapphire. The Marathon has a nicely domed acrylic crystal so if you scratch it a tube of Polywatch and a buffing cloth will take care of that!
I don't have a comparable Seiko quartz so I couldn't say which is better. However, their mil style auto is a sweet little watch in your choice of color for very little money :-!
I hope this helps,
Griff