I've got the both the Samsung & the WD Blue. I can't speak in terms of multitasking yet because I'm putting a new systems together with them and hadn't gotten a chance but I did run HD Tune for kicks and as mentioned by PC_user the Samsung is the fastest and the WD isn't far behind. My samsung tops out around 145MBps while the WD was around 125MBps I believe, give or take. Access times were similar.
If speed is your primary concern go samsung, if you want long term reliability for your important files go WD Black, they have a list long of features built into their drive that samsung can't even touch, their RMA is also better, and you get a 5 year warranty. The speed diff is also as you can see not that much. I would also assume WD Black will be better at multitasking with it's dual processor.
Also, the Samsung is a good deal quieter when seeking but there is a constant low volume high pitched whine. The WD is louder when seeking, but very quiet when not in use. Just my results so far. In terms of building my first super quiet pc soon, the WD I don't mind and will be muffled by acoustic foam in my case, the samsung hopefully will be muffled as well otherwise I'll sell it.
The straight answer would be a 150GB VRaptor. However it costs $160, for that amount of money you'd be an idiot not to get an SSD; 30-40GB for $100-120 or 60-80GB for $180-250.
Having your OS, apps, and some games on the SSD (with the rest of them on a HDD, along w/your data), beats the hell out of not having a SSD at all... And you can use symbolic links to shift game installs around w/o screwing up the install (or even individual games out of your Steam folder). Honestly they make such a huge difference, they've literally made VRaptors irrelevant.
However if you were just looking for a single-drive option within a limited budget, then the SSD is clearly out of the question (as you'd need to buy it + a data drive), and so would the VRaptor. In that case go with a 1TB WD Black or 1TB Samsung F3 as others have suggested. You'll probably find them priced within $10 of each other... Samsung's faster (500GB platters vs 333GB), WD has a better warranty, FWIW.