It really depends on how much tweaking you are willing to do to get the best picture quality out of your TV set.
Samsung is known for making televisions that are less than optimal at their default settings - for example, extreme over-saturation of colours and over-emphasized deep black levels that cause significant loss of fine detail. Samsung TVs can be tweaked to death, though. You can go to avsforums to find optimal settings for many different Samsung models.
If you prefer to pick a TV that's good to go out of the box, my personal recommendation would be for either a Sony or a Toshiba set. Both of these manufacturers make well-rounded TVs, with Sony having a slight advantage in picture quality. Sony default settings tend to over-saturate colours a bit, but not to the Samsung extreme. Toshiba sets keep "enhancements" to a minimum in their default state. LG is similar to Toshiba in this regard, but in the past I found their picture quality to be inferior to both Toshiba and Sony.
The arguments for and against 120Hz or higher TV sets are numerous; I'd rather not go into it. Some people like the creamy smoothness of interpolated 120Hz; I personally don't and have interpolation switched off on our TV for external devices. One advantage of 120+Hz TVs, as has been mentioned, is that they can faithfully reproduce 24Hz film material without the juddering caused by 2:3 pull-down. Some of the 120+Hz TV sets offer so-called 5:5 or film mode options where they repeat each frame of a 24Hz source 5 times, rather than interpolating, giving you a more "authentic" film look.
It should be mentioned in relation to the 120Hz vs 60Hz issue that some 60Hz TV sets also offer true 24Hz support. They typically achieve this by dropping the panel refresh rate to 48Hz and showing each frame twice.
With your budget, I think "smart" TVs are out of the question, so I'll skip that topic. USB playback features might be present, though. Samsung offers very good support for various video/audio formats and subtitles. Have a look at their manuals on the Samsung website. LG is close second. Japanese brands like Sony and Toshiba offer limited support, usually only for "industry" formats like AVC-HD and MPEG-2. MKV may be out of the question, as is subtitle support. I would not trust Vizio with USB. A Vizio TV set I used for a while was supposed to offer media playback via a future firmware update. One year after purchase the firmware update was still missing in action.
Anyway, my vote goes for Toshiba, closely followed by Sony. If you're not afraid of tweaking and want extra USB functionality then go for Samsung. It goes without saying that you should have a look at the TV in action before you buy.
P.S. Be aware that Samsung has an ongoing quality control issue with power supplies failing in their TVs.