Equi-Royal and HDR synthetics should be avoided. They are very low quality. Tekna is another brand that is good. They are relatively new to the market. I have a Thorowgood and a Wintec in my tack room and I have to say, the Thorowgood is nicer.
Wintecs get a lot of crap from a lot of people, but I love mine, it's been perfect. I'm not the best at cleaning leather, and I needed a saddle that could fit multiple horses in many stages, so it was the perfect fit for me. Sure, they aren't as comfortable as leather saddles, I'm not goint to lie about that, but I've gotten to the point where I can ride in any saddle, from Albion to Wintec, and it doesn't affect my riding much (unless it's too small). I've never owned a Thorowgood, but did use one and didn't like it. I've never ridden in an HDR synthetic, but LOVE my leather saddle from them, so maybe their synthetic is decent too. Here's a good website for tack review: http://www.horsetackreview.com/
They have plenty reviews there for all kinds of saddles.
Personally I prefer Wintec for English riding, all my saddles are wintec, and I am currently saving to buy a synithetic jumping saddle from someone I know :) I find that Thorowgoods are very hard in the cantle and seat. Not saying they are bad saddles, and I would ride in one if I had to, but I find that Wintecs are ALOT better!