Both have dust filters and on the 300r it's much easier to remove, the bottom just slides out and the front snaps off. You don't even need to move the case. On the lexa s you have to tip the case to get to the bottom one and the front is screwed on with the fan. Not to mention when you take off the front panel to get to it, the front has all the wires connected to it.
Aesthetically the 300r is better, but that's a personal opinion and looks is an obvious choice by the buyer. All that plastic on the lexa makes it look cheap and the front door just for looks is a pain in just about every situation. You even have to open it to get to the power button. The 300r windowed is cheaper everywhere I look. $63 at ncix whereas the lexa is $80...