i lost my greencard but i am qualified to apply for citizenship. should i just apply for citizenship or apply for replacement GC
You don't NEED to get a new greencard, but without it you don't have proof of your legal status which can be a problem these days of stepped up enforcement, especially as I note you are in Maryland (like myself). Further, you will not be able to travel internationally and return to the U.S. As USCIS Baltimore is processing citizenship apps very quickly, if you chose to forgo the I-90, you should get your N400 interview in less than 3 months.
Your call, I would recommend renewal.
In general, you do not need to file for a replacement card before filing for Naturalization. You should consider your specific facts, including, but not limited to your need to travel or to document employment authorization, and the strength of your Naturalization case before deciding whether or not to file.