Both are very good budget headphones at their own rights, I think you can't go wrong with either of them. I personally chose to go with the HI 2050 because it seems to be much more sturdier than the Superlux (metal versus plastic). It could be easier for us to give recommendations if you can list out your favorite music genres. For me, I usually listen to rock and metal, and some classical every now and then, the HI 2050 does a decent job for those genres. Beware that it might not be suitable for EDM, cause its severly lack sub bass and the highs will be unbearable at least for my own listening experience.
Also, I generally with what Me X3 has said above. Being an owner of all 3 DT880, DT990 and HI 2050, I too find that HI 2050 leans toward the sound signature of the DT880 more than that of the DT990, but with more mid bass and slightly more present mid range. If you do purchase the HI 2050 later, I strongly suggest you insert some ethernet cables inside the earpads. That will raise the distance between your ears and the drivers, providemore soundstage and reduce the heat.