Jen, I have used both. I like the Top Hatch you can hatch more eggs in it but it makes more noise and the light flashing disturbs some. I have had good hatches in mine and now that I have used the Lyon Tx6 I realize that the problem getting the humidity up was due to not adding enough water.
The TX6 is dead on accurate, you can't hatch more than around 16 bantam eggs and realistically 12 standard eggs. It is a piece of cake to use. The design is so simple but so effective. There is a big price difference if you get the turner, which is not essential because you don't have to open the incubator to turn the eggs, you simply turn the same handle as the machine does. The only down side to the TX 6 is cleaning is a bit more difficult. Fuzz gets up in the area of the fan and you have to unscrew the fan part and it is a bit dicey. If you are shooting for reliable temp and humidity control, then the TX is the best. You don't need to open it except to candle. Keep in mind that the whole incubator lifts off the tray and when you do that your eggs are just sitting on a tray in the open air so you don't want to be a compulsive candler. It does come back up to temp very quickly and humidity adjust quickly as well.
If number of eggs, ease in cleaning and overall economy the Top Hatch can't be beat. I made a cozy for the tub on my Top Hatch out of bubble wrap. In the winter especially it came in handy in keeping the temperature more steady.