man there are tons of threads on this. Look in the Modify section and search for it. Generaly the best speakers are the ones that fit your budget and type of sound. If you want more rap/hip-hop style music, then go with titanium tweeters. If you want more country/pop music, then go with silk tweeters. In a boat, the most important thing is Bigger speakers and more Watts. You don't have a cabin, like in a car/truck, to bounce the sound in, so you need to make a lot more noise. Get speakers that have good RMS ratings and match them up to a good amp. You can prob go up to a 8" speaker in your boat, but you need to measure first. Most MFG's sites will list dimensions for their speaker holes and grill sizes. Look at my builds(cycleguy88), RFoster130, badconexun, davo, and a few others.
