I would take the 777 in 1st ; it may not have the showers but the cabin is smaller and I find that the service can be a bit better; the suites are as close to being the same on 380 vs 777 as to make no difference

On SYD-DXB , I have also found that the evening 380 flight can be close to full whilst the non stop daytime flight only has a few 1st passengers

The shower is a nice feature of the 380, but for me the 777 is the better option