To echo just about everybody else, the rules difference that leaps out is the armor/toughness thing. Blue Rose uses the typical D&D mechanic where armor makes it harder to hit and your toughness increases with level. True 20 uses the Runequest (I'm sure there are many others) mechanic where armor is damage resistance and you get harder to hit, rather than tougher, as you rise in level. As I was working on converting Runequest to a BR/T20 type system, I picked up the True 20 PDF and was mostly impressed. As for the magic system, Blue Rose's is a bit more complex, and it feels like a complete (if fairly campaign specific) magic system. True 20's is simpler and highly generic. While there is nothing wrong with it per se, I don't think I would ever run a campaign with it unless magic was very rare, as there would not be enough variety to keep it interesting.
As for a recomendation, I was a bit surprised to see True 20 go for the different armor mechanic that Blue Rose. Or perhaps I should say that I am surprised that few other d20 games have doen this. When one looks at the overall effect of the armor/toughness rules, it works out this way: In Blue Rose, armor is great for fighter types at low level, but since you get an increases dodge bonus as you go up in level, and since armor in BR has a max dodge value, characters will want lighter and then no armor as they increase in level. This is a bit odd if you think about it too much, but I like how it lets armor be necessary for soldiers, where heroic, high-level fighters don't need it as much. In T20, on the other hand, your defensive bonus increases faster that in BR, and is unaffected by armor. However, armor doesn't really absorb damge like in a system with hp, it provides a toughness save bonus, so there is no threshold below which you can completely ignore damage. This means that 1) armor is effective at all character levels. Whatever armor your character likes at first level will likely be what they always like. And 2) since armor is merely the easiest way to increase your toughness save, and your main defense should be to avoid being hit, the end would be that armor nearly always helps, but is not a virtual requirement. Not having played T20 much, I can't say for sure if this is how it works; unlike in BR where one can easily calculate which armor one should wear. I don't know if this helps you at all, but hopefully it give you a bit more info for the decision.