Non-saxophone players look away now ...
I'm mainly a tenor player and my weapon of choice is a P. Mauriat PMXT-66R. It's got a well balanced tone and pretty even intonation, and it just feels really solid under the fingers. I've never got on with horns that feel too delicate or flimsy and my Mauriat has always felt really comfortable. It just seems to let me make the music I want to make without getting in my way or telling me what to do! I've customised the palm key positioning and venting a little, tightened up the action and I've also fashioned a bespoke high F# key raiser to allow for ease of access throughout the altissimo register. In all honesty, if you offered me a Mark VI then I'm not sure I'd be swayed.
On the end of that, I put an Otto Link ebonite mouthpiece with a size 7 tip. A new mouthpiece is always the first place to look if you're after an upgrade as it's a lot cheaper than a new instrument and makes a really huge difference to the sound and feel of your setup.
I've used Francois Louis ligatures on all my saxes for years. I think players often overlook the impact that their lig. has on the overall tone and playability of their horn, but I think it's almost as important as reed choice,
Talking about reeds, I've tried pretty much everything on the market and I've settled on Alexander NY 3's. Alexander reeds are by far the most consistent I've ever tried (I rarely find one that doesn't want to be played straight out of the tin!). Apparently the NY reeds were developed in partnership with the late, great Michael Brecker and that says more about them than I ever could!
As a doubler, I also play a Yamaha soprano sax with a Selmer mouthpiece, a Yamaha flute and a Buffet clarinet with a Rico mouthpiece and BG France ligature. I've also got a bass clarinet and another few bits and pieces knocking about somewhere too! I use Legere Signature reeds on all my doubling instruments which is mainly for practicality (I just need to know that they're ready to go whenever I need them) but I do actually really like them too. I recommend giving them a try but I've found that it's worth going down a strength if you do.
Having said all that, there's absolutely no amount of money you can spend that will improve your sound more than practise! Long tones, harmonics, dynamic exercises, articulation patterns and intervals are by far the cheapest way to sound your best. If you really are convinced that your horn is holding you back then go and buy something better, but beware of searching for quick fixes!
And finally ...
I also have my "Glow-Sax". but that's a bit more of a trade secret! I will say that I play it through a Selmer Soloist mouthpiece with a Legere Signature reed and a Francois Luis ligature, but if I told you anything else then I'd have to kill you. ;)