Just got a new Sony 55" a few weeks ago, 2018 model. At first all seem to be the same (LEDs), but there are some pretty noticeable differences - refresh rate, backlit, OS etc. A pretty good site to compare them:
https://www.rtings.com/tv/tools/table/23374
Please note that the model name varies from continent to continent. Its a Canadian site, so sometimes its hard to find the things they sell here in EU.
Currently the cheapest LED you can get what will be the closest to an OLED (dark blacks, colors wise) is the Sony X900F (in EU its XF9005): FALD (Full Array Local Dimming), 120hz, HDR10, USB3 (in case you want to record something).. comes in 49-85"
But it comes down to what will you be watching in the end. If its just regular TV broadcast then anything will do it. If its Netflix (with solid Internet connection) or BluRay then I guess you will need HDR(10) too. And if you watch your TV during the night with lights shut in the dark, then FALD is also a nice feature to have.