The best advice I can give is to get speakers that are efficient. When I used to install stereos people would pick speakers because they handle 200W! However, only running 50W they didn't always sound good. However a nice quality pair of the same size speaker that is rated for 75W sounded much better on the 50W being delivered. Also keep in mind your head unit output is overrated. Your head unit will likely never put out the 55W peak it is rated at. I would doubt 20W rms is even good, but not too far off. Just remember these things when looking at speakers.
Also, I have never seen a speaker blown from too much power. It was always from clipping and distortion from people turning things up too loud. This is more of a problem when the speaker is underpowered. I would not be concerned with overpowering a speaker.
I personally like Infinity speakers. I have also had some Polk that were really nice as well. A good clean balanced sound. I was never a fan of JBL. Their highs always seemed harsh and too "bright" and had to adjust amplifiers and equalizers to try and tone that down. Alpine aren't bad either, but I have never personally had a set in my vehicle.
Much of this is personal preference. Go to a car audio store and use their demo setups. See if you can listen to some speakers that are connected to a headunit with similar power output as yours and no amplifier. See what you think of the sound. What you like is what matters. If there is an amplifier used the speakers will sound different than just off of a head unit.