Having XV8s as troops is a blessing as far as I'm concerned, though if you're not careful they can start to get stupidly expensive. So how do you get them to work? I've thought about it and I've settled on burst cannons, here's why...
I asked myself: What are troop choices for?
A: Securing objectives
Unless you're planning to simply table your opponent every game (Death Company!) your troops are generally going to win you the match by securing those objectives and their corresponding victory points. To do this, troops need to be durable but still be able to deal some damage. This is why tactical squads are to my mind one of the best troop choices in 40k. So I asked myself, how can I get my XV8s to function like tactical squads?
Now, durability is a slight issue with this unit because there are only 6 wounds in a maxed squad of 3. The solution I think is to give each XV8 a drone or two, for my money you're better off giving XV8s a pair of shield drones as this gives the whole unit 4++ and essentially giving each suit 4 wounds. 4x3=12 wounds
Firepower is where Crisis suits excel but the humble burst cannons are often overlooked. Burst cannons are 18" S5 AP5, Assault 4 so compared with much of the Tau arsenal they seem clumsy and ineffective. In an elite slot I agree with that sentiment but in a troop choice they start to prove their worth. Arming all 3 with twin-linked burst cannons gives 12 re-rolled shots, however for an extra 15 points you can give them two burst cannons for a total of 24 shots. Now, balance of probability states that at BS3, 50% will hit, therefore...
Twin-linked: 12 shots = 6 hits, re-roll 6 misses = 3 extra hits for a total of 9 hits
Two sets: 24 shots = 12 hits
Your extra 15 points gives you an extra 3 hits, which for my money is a good investment.
But, you may say, having twin linked burst cannons means you can put another weapon in slot 3 and use it! Well, yes it does but I've got a solution to that too. Flamers. Give each XV8 a flamer in their 3rd equipment slot, not for offence, but for defence. Charging into a unit with not only 24 overwatch rounds but also 3xD3 wall of flame shots is going to make anyone think twice about it.
As a troop choice, this gives you a reliable, highly mobile unit that can take and defend an objective for about 200 points. You also don't need to give them that heavy, tank busting option because you should have enough other Battlesuits knocking about to deal with any heavy stuff. These are objective takers not dragon slayers - it's an important distinction!
Two sets of these should aim to secure central objectives while another team of XV8s armed with missile pods should hold the home objective. Tool up a squad with fusion blasters and shield drones to go tank hunting or some plasma rifles to take out elite units. These are all now troop choices, freeing up space (though not points - if you take the 4 squads I've described you're looking at 800-900 points) for Riptides and the often overlooked Stealth Teams.
This is all hypothetical but it makes sense on paper, I'll let you know if it works as and when I get round to buying, building and getting some games in.