What about the Koralia do you not like. I have one and from the looks of it, it's a great pump. Nice open flow, great for mixing salt. lol, but the size of it is what draws me towards the Vortech. In fact, I have an MP20 coming in the mail. I'm going to do the upgrade/convert it into an MP40 since everything is the same except for the driver and power source. Never had any experience with Tunze pumps but plenty of people have told me that they are reliable. Again, it goes back to size, given you can get a few Tunzes for the price of one Vortech.
I guess I'll figure it out once I get my pump. I'll be using it as an MP20 and converting later. If anything I can always sell it and buy two Tunze pumps for about the same price (6025.) Either way you can't go wrong with them. Oh yeah the 6025s can be modded for more flow in case you need it.