I've personally worked with many females partners. All of them did their duties correctly and effectively. All of them were small and petite, and when we lifted patients, I always opted to take the heavier head side of the patient. We just put our pride aside and did what was best for both the patient and the EMT. I know she would fatigue quicker by grabbing the head side of the patient who was on a flat, so I take the head. It wasn't sexism, it was common sense that I could lift more than her. I don't want either my partner nor I to get injured because one of us was too prideful to admit that we could not lift a certain patient. I think it made sense.
Regardless, most of the female EMT's I worked with took their jobs seriously. I don't think you should be discouraged to work in this field, and I would actually encourage you to pursue it. The last female partner I worked with had such a vast knowledge of EMS and techniques. I learned more from her in one shift than I did with any other partner, regardless of gender. I am fairly new, about a month or so under my belt, so I have had the opportunity to work with many different EMT's. Male, feamale, tall, short, fit, overweight, black, white, you name it. I did however notice that medics, FD, nurses, and anyone we came in contact with were especially polite and willing to help whenever I worked with a female partner. Which is actually why I prefer to work with female EMTs. If only everyone treated me with the same politeness, regardless of the gender of my partner.
Personally, I always keep it professional. I believe a lot of EMT's are the same way. Of course, you will get the occasional sleeze, but I think that happens regardless of where you work or what field you work in. Just be the best EMT you can be, and take pride in what you do. Being a minority in EMS should motivate you to work harder and to prove to the patronizing aholes that you're damn good at your job.