I'm going to go against the curve
If you are the type who keeps their phone for the full two year contract (honestly I am not sure how Tmobile works now so that may not apply), I would think waiting what might only be another 3 months might be worth it to do. Like others have said, the upgrade likely will not be a major upgrade. However, it is almost a given that the camera and processor will be improved. Perhaps battery life as well? Maybe more storage? Added security features or NFC? Truth is we won't know for sure until Apple takes the stage. But be sure to ask yourself, if you get the 5 in a few weeks, and the 5S is indeed released at the end of June with any of these additions, will you be kicking yourself for not having waited? If you do not think so, then get the 5. If you feel you might wish you had waited, then hold out a little longer since it sounds like your current device is capable, just not ideal.