I'm trying to decide what fleet to scratch build as my opposing force. Orks are the obvious ones, but Tau have sort of a generic sci-fi look I could use a lot of the dime store ships with. And obviously I'd want both sides to be playable. I know Necrons are just a terrible bit of rules writing and overpowered, are Tau and Orks OK?
Necrons aren't actually that bad -
Provided you've got the right version of the rules - the ones in Battlefleet Gothic: Armada, rather than the original version in the
BFG magazine.
The ships are still harsh as hell, but are much more beatable - the huge point bonus you get for hulking capital ships, for example.
At the same time, they do violate a lot of 'basic'
BFG rules, so they don't make it easy for a player to learn. And they really, really do unspeakable things to Eldar or Dark Eldar fleets.
Of the two you've listed, I'd probably say Tau. Tau fleets (the basic one from Armada) is a pretty fair match for the Imperial Navy. You lose out on battleships, but get cheap supercarriers with awesome bombers. Your 'line cruiser' has less guns, but is able to point almost all of them forwards to get more firepower in a single ship-vs-ship engagement. Your light cruisers are better armed but much less manoeuvrable. If you want to play 'normal' scenarios, the Imperial Navy and Armada Tau fleets are a pretty close match. You will need a LOT of torpedo markers for these two fleets, by the way.
Orks are an effective fleet BUT they have problems. Don't just use them for a 1500 point 'pickup game' because they'll get murdered, again and again, until you join the chorus of 'Orks Suck in
BFG'.
BFG orks are a raiding fleet. That, plus their higher-than-the-imperial-navy attack rating, means you should, most of the time, be playing raid scenarios with the ork player as the attacker - this goes a long way to making what look like weak ships suddenly be much more effective.
The Terror Ship, for example, is a so-so carrier - Fighta-Bommas are not a substitute for 'proper' attack craft, and whilst tough it's not that well armoured, has mediocre guns and its shields are poor. However, in Cruiser Clash, it comes into its own, because it's just about the only carrier
any race has the option to buy with the 185 point limit, and certainly it's the only cruiser-class carrier, with double the launch capacity of strike cruisers and defiance light carriers.
Similarly, the Savage gunship is mediocre in an open fleet battle. In convoy attacks, where a squadron can appear from a 'contact marker' and move into range on a head-on strafing run that turn, an escort with 4 eavy gunz becomes a terrifying prospect.
