E-Skip signals usually exhibit rapid fading, from being very strong to very weak or non-existent, and then being very strong (like local strength) again. Tropo can be strong, but the fading is often slower, and in my experience E-Skip produces better signals on FM than all but short tropo.
During any point in an E-Skip opening, there is a maximum usable frequency (MUF), above which there will be no skip signals. The MUF rises and decreases during the opening, and how high it reaches varies greatly between individual openings. Often observers first notice a skip opening in the 10m ham band or on CB radio (27-29 MHz). Then, if the MUF increases enough, distant signals will begin to come in on channel 2, 3, 4, 5, 6 (assuming that these channels are free in your area; otherwise you might see a line pattern, or even a distant signal superimposed over your local station), and finally, if you're lucky, up through the FM band. Occasionally, the MUF will go all the way to the two meter ham band (144 MHz), Weatheradio (162 MHz), and very rarely, to high-band TV (channels 7 - 13). Signals near the MUF are normally in the 800 to 1,300 mile range; up to 1,600 miles or so is possible on a single hop. The farther below the MUF, the closer the signals propagated will be. Low VHF (ch 2-6) TV stations from under 400-500 miles, or FM stations from under 500-700 miles, are quite rare. So to hear something 493 miles away on FM via E-Skip would be far more significant than hearing something 1,393 miles away.
Tropo, on the other hand, doesn't really have a "MUF", or at least not one that is significant for TV / FM DX'ers, but it tends to affect the UHF TV band the most (which is never propagated by E-Skip), followed by the high-VHF and FM bands. The effect of tropo is diminished on the low-VHF channels, though they can still travel quite a distance during a good opening - I've had St. Louis on channel 5 and Davenport on channel 4 from Duluth during exceptional tropo openings. Tropo distances are normally shorter than those experienced with E-Skip. Here, for example, always-present troposcatter and often-present "enhancement" bring in stations up to about 300 miles away. Beyond that, there's tropo ducting. The most distant tropo ducting signal I've seen was KSPR / KDEB from Springfield, MO, 660 miles away. Over land, tropo beyond 500 miles is "very good", though not especially rare; beyond 800 miles or so you're into the "extremely good" category. It's a different story over water, especially over the Gulf of Mexico, where FL - TX openings are not rare.
