It depends on who you ask. If you ask a CZ guy, he'll tell you the CZ. If you ask me, I'll tell you the Excal. Actually, I have an Excal 1000 and a CZ-70. The Excal is a little deeper than the CZ at the beach and the threshold makes it more likely to help you snag an "iffy" target that might get missed by the CZ. The CZ-20 is probably sturdier than the Excal. The Excal is more sophisticated with it's 17 frequencies to the CZ's 2 frequencies and it's multiple tone ID system compared to the 3 that the CZ gives you, one of which is iron. So you get to know the tones on the Excal and you have a WHOLE LOT better idea what you're digging. Of course if you don't care and want to dig everything, then it doesn't matter.
As for the choice of Excal, if you will be mostly in the wet sand I would get the 1000 because the bigger coil is desirous for better coverage. If you were going to be more in the water then the 800 would be the choice because it glides through the water a little easier.
Either way you go, you won't be sorry. But the two machines are very different and it would be a really great idea if you tried to check each one out before buying one, to see what you think. More than likely, ONE of them will stand out as the better choice for YOU. You might try the local detecting club...just about can guarantee that there are one of each in the club, if not more.