Wow, this is weird....
A couple months ago, I was bass shopping and had narrowed my choices down to the exact two basses you're looking at!
I went back and forth for a while, and got the GSR200. I really love the look of the SR300M - the light color of the fret board and the color-matched head stock are awesome. Reading reviews on both of them (mostly at guitarcenter.com where I bought mine), some of the reviews said that the pickups have a curved shape to them, and that the low string lacks punch because it's further away from the pickups than the rest of the strings. I have not actually played the SR300 to verify this for myself, but considering a few different people - on a few different sites - mentioned this, my guess is that it's a legitimate concern. That was the only minor nitpick I could find in any review of that bass. From everything I gathered, it's otherwise an outstanding instrument. And you could always swap pickups to cure that problem - if you would even consider that to be a problem. Although a few reviewers pointed out a lack of punch to the low string, I suppose it's still a matter of opinion. But I'm not sure that you could lower just that string without messing up the action and introducing fret buzz. But Ibanez makes great gear, and I'm sure it's worth every penny of the $300 price tag at Guitar Center.
As for the GSR200...
I absolutely love this bass! There is literally nothing that I don't love about it. Don't let the $200 price tag fool you - it plays, sounds, and looks much more expensive. Read reviews on it. There's really nothing negative to say about it.
The action is low, making it very easy to play. The tone is outstanding, and the tone control knob has a huge impact on the way it sounds. On my guitar, I keep the tone controls all the way "bright". On the bass, it sounds great at any setting, and allows a lot of control depending on what you're playing and personal preference.
The Phat bass-boost knob is awesome, too. It's powered by a 9-volt battery, accessed from the back side of the bass. It does exactly what it says it does - it add a lot of deep low end punch. The bass sounds great even with it turned all the way down, but turn it up a bit and you get some serious thump. It's a great feature to have.
I still consider myself to be a beginner bass player, but I'm learning fast and it's coming a lot easier for me than playing the guitar has. Even a garbage bass can sound good if a great player is playing it, but it helps that this bass has such great sound, as well as fit and finish. It actually encourages me to play and improve, because I haven't seen any limitations to this bass. Finger, pick, and slap work all sound outstanding.
Unless the slightly more expensive-looking looks of the SR300 are important to you, I'd go with the GSR200. You will NOT be disappointed. This is the only bass I own (and with this bass, I have no need to own another) but I have played much more expensive ones. Honestly, this one is by far the best.
Sorry for carrying on about it. I just never really got to gush about how much I love it before. If you have any other questions about it, feel free to ask. I wouldn't change my decision on getting the 200 for anything in the world, but it still would have been cool to talk to someone about it who actually owns it.
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