Rob Alen gun
I use a 1.3m Rob Allen railgun - a euro gun - with a single 20mm rubber. It's short enough to take into kelp if you're carefull, and big enough for bluewater. I've taken quite a few Tuna on it, both Bluefin and Yellowfin, best being 37 Kg yellowfin. I also regularly shoot large yellowtail with it, up to 15kg's. Tuna have a tendency to bend the shafts, but I haven't had anything else bend it.
The only problem I have with the current shaft is that the shooting line runs through the spear right at the back, behind the notches .... not a good idea. I'm getting a new shaft before the weekend, this one won't have the same problem. I've asked them to put the hole in front of the notches - this still makes the shaft as streamlined as possible, but with less chance of snapping at the notches.
I've used a Riffe Blue Water a couple of times, but wasn't that impressed. It's slow to swing and track, especially if you're after big and fast predators. It did however have the power to knock a buffalo over. So I guess it's a compromise - I prefer better tracking, although there's not that much of a difference in power. You can also add two rubbers to it, but that would be overkill in my eyes .....