Yes, HL has improved. No, they're no where near Tamiya. If you want a solid tank as an RTR from the box, go with Taigen. But, research them first. Most are much improved versions of HL tanks. Some are basically just HL tanks with a better paint job and better electronics. I would only get an HL if you know you want to do major work on it that would have you hacking up the Taigen anyways. Or, if you're looking at getting one that Taigen hasn't really upgraded. That's why I went with an HL PzIV when I did that build. Taigen hasn't done much to upgrade that one and I knew that I would add a lot of tweaks - Taigen, Asiatam, Mato, etc - that didn't justify the extra cost of the Taigen.
Oh, and I like my airsoft. So, as good as Tamiya is, it's not on my list to buy.