So let me ask a couple of questions to help you.
1) How important would it be for you to hear an announcement of say, "30 seconds left"? The Spektrum DX6 (not the DX6e) has voice capabilities and a speaker that will announce this. The Graupner has it, but you would need to put in an earbud or use an additional Bluetooth module to use it.
2) How easy is it for you to get Graupner receivers? I understand you get 2 with your offer, but if you go to a local hobby store, are you able to purchase receivers there, or is it online only? It may not be a big deal for you, but if you want a new receiver and can't get one easily, it might color your opinion of the receiver.
3) For that matter, how are you getting support for the radio you choose? Is there a group at your local flying field or in your area that's familiar with Graupner or Spektrum? I know this is one of the reasons I went Spektrum with my choice - most of the people at my field and my father's field fly with Spektrum because that's what they like. This does not in any way mean that the Graupner radios are inferior; I saw a demo of them at the AMA Expo in January, and liked what I saw. But, nobody I know flies with it, so my support is limited to what I can find online - I'm having to read, re-read, and teach myself how to configure the radio since there aren't people around me who have knowledge of it.
4) Which feels best to you? When I was first getting into the hobby, I had the opportunity to go with either an FrSky Taranis radio, or the Spektrum. The FrSky radio was about $50 cheaper than the Spektrum DX6 that I was looking at, so I asked the salespeople if I could handle the radios. They pulled out both, and the FrSky's gimbal controls felt a lot looser to me than Spektrum's controls. I was told I could upgrade the gimbals, but the cost would be $50, and at that point, it was the same as purchasing the Spektrum, which I felt was better for my needs. This, I'll be honest, is more of a user preference thing, but if you plan to do a lot of flying, find something that feels comfortable to you - no sense getting hand cramps or having unresponsive sticks to control your flights.
Ultimately, buy what suits YOU best - whether that be Graupner or Spektrum. I like both, but my personal preference is Spektrum because I can go into my local hobby shop and buy a plane that already has a Spektrum receiver in it and just bind it; if I want to build a plane, I can buy a Spektrum receiver from that hobby shop and not have to wait for delivery. But, that's what I find works best for ME.
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