I haven't used the NT1a in a very long time, but the issue I remember having with it was being pretty cold and not having a firm core to the sound. The NTG-2, on the other hand, sounds awful. I've never actually used my own even though I got it for free from a friend (I did give it the benefit of a doubt when I first got it in the studio alright to see if it could be used for anything, but gave up completely on it and put it away never to be actually used for something), but I did work on it a lot (others gear) before I could afford the good stuff. The sound is very muddy, and it sounds phased and lacking any real top whatsoever with a very unclean mid. If I had to choose between them two, I'd go for the NT1, but better yet, the extremely cheap but very good sounding mic Line Audio CM3 gives a tremendous bang for the buck! I gave about 100 Euros for mine, but this was in the late 90's/early 2000's somewhere when it was just release. Should be about the same now though.
I don't know that Alesis interface per se, but if it's noisy, than Studio Projects VTB-1 is a good choice to replace the internal microphone amplifiers. The extreme top is so-so, but the sound below that sounds really good for a mic-preamp this cheap. I use two of them myself for several things, I kinda like the sound of them, though the valve-option isn't very impressive. Would probably be much better with my Telefunken-valves, but I don't know how to calibrate it afterwards...but as the solid state mode sounds as well as it does it really doesn't matter, though the blue glow from the grille does look nice in the studio!
But a microphone that could really make a difference is the Sennheiser MKH416. It's still the favorite for many of us, me included, but because it's so incredibly old (for a piece of gear), it's nowadays pretty cheap compared to what you get. Still not a budget mic as such, but not unreachably expensive either.