As it looks like this won't get an answer (presumably because they are as good as one another/no one has tried side by side) I thought I'd update with what I did.
I used the Paella rice because it had a shorter grain and Japanese rice also has a very short grain.
All the recipes I found online (I browsed about 5/6 of the top results) said to rinse until the water is clear so (sorry GdD) but I ignored the advice above for the most part. I needed to wash about 8 times before I gave up - the water wasn't completely clear but it was better than it had been.
I then soaked the rice for a couple of hours (because I had time) but most recipes agree that you should for at least 30 minutes. I then drained and added cold water at a ratio of 1:1.7.
I put the rice on the stove with a lid on and brought it to the boil.
I boiled for 10 minutes and removed from the heat and let it sit for another 15 minutes. It's apparently important that you don't remove the lid.
I added a tbsp of mirin per 300g of rice and 'fluffed-up' the rice with a plastic rice spoon.
The rice was definitely sticky and there is no way I would have wanted it more so (in fact it was probably slightly too sticky) so I am very glad I washed the rice and will probably try rinsing a couple more times in the future.