These resources are my go to when researching gear. Just keep in mind that you should read reviews from multiple sources so you can get a well rounded view on whatever it is you're interested in. Just because one reviewer does or does not like something doesn't mean it's right or wrong for you. Above all, keep in mind the context of the review and reviewer. For example, your looking for a portrait/landscape/low light stills camera and the reviewer mentions that
a) the camera only shoots 5 frames per second
b) the cameras video features aren't very good
does it really matter since portrait/landscape/low light photography typically doesn't require high frame rates like sports photography would, nor would video necessarily be a key feature/requirement. No piece of kit is great at everything, so perhaps the question then is, "Does it meet or exceed my requirements for what's important?"
- DP Review - equipment reviews
- DxO Mark - sensor & lens scores
- Sensor IQ - studio shot comparison images
- Tony & Chelsea Northrup - reviews & education
DP Review provide detailed reviews on gear and is useful for news about what's going on in the world of photography. If you're looking for gear, DP Review should be on your list of sites when researching that new camera, lens, tripod and so on.
If you're upgrading your camera body, I've found their Studio Shot Comparison tool very useful to judge what sort of image quality improvement I can expect, after all, if you're not getting a better image, are the new features alone really worth it.
DxO Mark has been my go to resource when researching lenses to suit a specific camera body, in particular the sharpness of a lens. Note that the same lens on a different camera body will perform differently, so it is very important to compare lenses on the camera body or bodies you have or intent to buy.
From personal experience I owned a Canon 650D which has an 18Mpix sensor. When I researched the very popular 70-200mm focal range, it became obvious that those lenses, while producing fantastic results on a full frame body for which they were designed, would actually perform quite poorly on the 650D, eg. the highly regarded Canon EF 70-200mm f/2.8L IS USM would only be able to resolve the equivalent detail of 10Mpix..!! A good choice? NO, not at all. The Tamron SP 70-200mm F/2.8 Di VC USD would give me 15Mpix and when I upgraded to the Canon EOS 6D full frame body with a 20Mpix sensor would give me 18Mpix. A much better choice and cheaper to boot.
While DxO Mark provides detailed and scientific performance data on a variety of lens parameters, sharpness is the main criteria by which I judge a lens' performance. Tony Northrup has a great YouTube video on How to Use DxOMark: Lens Sharpness & Sensor Quality. On the issue of how to take sharp photos, I go into detail on my Education page.
As Dave Dugdale once commented, I don't upgrade my camera body for features/functionality, I upgrade it for improved image quality (IQ). Well, I agree, so with that in mind I prefer Imaging Resource over DxO Mark for comparing camera sensors as DxO Mark uses metrics like colour depth and as Tony Northrup highlighted, there isn't a modern camera that suffers in that department so it's a meaningless metric. On the other hand, a cameras performance is noticeably affected in a negative way when the amount of light is reduced or the ISO is increased. Imaging Resources' Comparometer allows you to directly compare carefully controlled reference images from 2 cameras side by side at various ISO settings. If you've ever wondered just how much better a full frame sensor is versus a crop sensor in low light, this is going to leave you in little doubt which is better.
Tony & Chelsea Northrup
Tony & Chelsea are a great source for photography education and regularly publish on their YouTube channel. They also publish eBooks such as Stunning Digital Photography and Photography Buyers Guide for which you pay once and receive all updates for free. There's also a bunch of YouTube video links on my Education page.