So I'm thinking about 300-400 for the price point.
I had seen a Samsung one which looked like a decent option
Samsung is a reasonably safe bet (safer than LG, IMO). I'd definitely buy though from somewhere that provides some additional warranty cover thrown in. Both Samsung and LG run their LED backlights quite hard to generate the screen brightness, and so these are showing up as a common mode failure. I'm not seeing the same issues with Sony or the genuine Panasonic models.
On paper, there's nothing much to differentiate the Samsung 43RU70102 (£299) from the 43RU7100 @ £320 aside from maybe a bit of styling and Alexa support. The picture quality id good for the money with Standard Dynamic Range material, but the sets don't have the extra light power or additional colour range to make HDR content pop off the screen. The viewing angles are said to be quite narrow too, so the colour saturation changes quite a bit when viewed even slightly off axis
The 43RU7410 @ £399 is a step up. The panel is capable of doing dithered 10bit colour, and that should make a bit of a difference when it comes to viewing UHD material with the bigger colour spectrum. The backlight is behind the screen rather than around the edge, and this gives the TV the ability to dim portions of the picture while other areas are bright (or so the spec claims). The panel brightness is still a bit limited though, and the viewing angles are narrow too. This means that there's not enough light power to make a noticeable difference when switching from SDR to HDR material, and the colour accuracy is only at its best for viewers sitting directly in the middle. Still, those niggles aside, it's a decent telly and IMO, if you can get by with the viewing angle and plan to watch a lot of streamed HDR content, then this is probably a top contender at £400 regardless of brand.
Looking at alternatives, Sony 4K UHD will take you well over your budget (KD43XG7003/7073 @ £480-£500), or you drop down to 1080p resolution with the 43WF663 @ £380. This one is a bit of a curious mix because although only 1080p resolution, it does claim to support HDR fir TV broadcast (HLG whenever we finally get it) and HDR10 which is for streaming and off-disc content from UHD BD players. The brightness is limited though, and that's down to price. However, the viewing angles are wider due to an IPS panel rather than the VA panels used in Samsung and Panasonic sets.
The LG 43UM7500 (£360) also uses a wide-viewing-angle IPS panel. It's backlit too but lacks a dimming feature. Being an IPS panel means the blacks aren't as deep as the VA panels in other brand sets, so viewing with a little room light on might be helpful. Tweaking the picture controls could help too both with the level of black and by not over-driving the backlights which are a bit of an Achilles heel in reliability-terms for LG at the moment.
The panel does do dithered 10bit colour, there's a better step up in brightness between SDR and HDR than the other models I've listed. Also, LG throws in a lot of toys with its tellies such as a satellite and cable tuner, Wi-Fi and what they refer to as their Smart Remote. (You can look that up for yourself)
The other two serious contender brands are Philips and Hisense. Both have limited HDR brightness (are you starting to see a pattern yet?) but reasonable to good SDR performance.
