I think Juwel have been in decline in recent years. They have had numerous quality control issues.
If money is not an issue, but whichever you think you like the best, unusual problem.
Without money issues, this...
>>> i'm looking to get a 20gal tank
... is your most limiting requirement. Larger tanks are always so much more stable, easier to look after and flexible as your interests in the hobby drift as they inevitably will. A crappy 55 will serve you much better then a flash 20.