In general: Gravity feed is easier to clean and probably better balanced. Bottom feed cup is larger (maybe). Gravity fed needs some sort of stand for filling.
To my eye, the Earlex looks to be a better made system. Metal gun, more robust, staged turbine. They both use a turbine which is similar to compressor driven guns. The Earlex pressurizes the material in cup which will help with material delivery rate, especially with heavy viscosity stuff. Air is also used to atomize material as it leaves the tip of gun and forms the spray pattern.
The Graco is an airless sprayer. These pressurize the material directly and forces it through an orifice in the tip, thus atomizes without air. The fan (spray pattern) is formed by shape of orifice. Airless can give really fast material delivery but usually not for fine finishing, although with right(small) tip might work OK. Think house painting.
In commercial shop settings the shizzle is air assisted airless sprayers like Kremlin or C A Technologies. Expect to spend coin far is excess of your budget and you need a bigger compressor
Honestly the Earlex looks like a pretty darn good deal, putting the emphasis on finishing smaller things as opposed to painting the house. You can rent an airless sprayer for pretty cheap and if you haven't used one, I dare say you'll be surprised at how fast it'll slurp a fiver of paint, but I've never used a baby like the one you mention.
