Hi there
First off you need to decide on an amp for your new headphones, as the headphones you mention definitely perform best when amplified. Fioo E10k is a good start!
Then you must decide which of these headphones suit your favourite music to listen to. Personally i'd strongly recommend the
ATH-M50X as they are the best "all rounder" in the price category that you mention. They have great bass and clear instrument separation.
The Beyerdynamic DT 990 250 Ohm will be harder to power as they demand more juice compared to the others. They offer a nicely balanced sound.
Now....the Sennheiser HD598's are definitely the more " audiophile sounding" headphone of those mentioned above. You may not like the open-ness of them. There is almost nothing behind the drivers so people will be able to hear what you play through them even at moderate volume. They are accurate and have better than average instrument separation
(due to being open-back).
So i strongly recommend the ATH-M50X for you as you may or may not like the open-ness of the Sennheisers. If you do like that kind of thing then by all means go for them. The DT990 250 Ohmns fall between these 2 in terms of sound quality. But as i said they require more power to sound their best.
There are other offerings out there too, such as the AKG K550 or K612 ( good for older recordings), the Denon ah-d1100 (good for Hip Hop) and the Creative Aurvana Live ( good for rock). Then there's my favourite unknown classic...the Pioneer SE-A1000... Comparible to Sennheiser HD650 but for less than $100...
Hope i could be of help!