不要选择Automatic也不要选择Metal，因为这个选项可能会导致app在Iphone6上出现crash。
一个类似的crash堆栈：
http://stackoverflow.com/questions/31803907/finding-cause-of-crash-sigabrt
Exception Type: EXC_CRASH (SIGABRT) Exception Codes: 0x0000000000000000, 0x0000000000000000 Triggered by Thread: 0 Thread 0 name: Dispatch queue: com.apple.main-thread Thread 0 Crashed: 0 libsystem_kernel.dylib 0x00000001964fb270 __pthread_kill + 8 1 libsystem_pthread.dylib 0x000000019659916c pthread_kill + 108 2 libsystem_c.dylib 0x0000000196472b14 abort + 108 3 libsystem_c.dylib 0x0000000196447a38 __assert_rtn + 88 4 Metal 0x0000000186b93b0c MTLReportFailure + 452 5 Metal 0x0000000186b6b24c validateWritePixels + 704 6 AGXMetal 0x0000000105994c44 0x10597c000 + 101444 7 AGXMetal 0x00000001059bc084 0x10597c000 + 262276 8 Metal 0x0000000186b6ce80 -[MTLIOAccelTexture replaceRegion:mipmapLevel:withBytes:bytesPerRow:] + 76 9 HitAndRescue 0x0000000100970208 TexturesMetal::UploadTextureSubData2D(TextureID, unsigned char const*, int, int, int, int, int, TextureFormat, TextureColorSpace) (TexturesMetal.mm:253) 10 HitAndRescue 0x000000010096b4e0 GfxDeviceMetal::UploadTextureSubData2D(TextureID, unsigned char const*, int, int, int, int, int, int, TextureFormat, TextureColorSpace) (GfxDeviceMetal.mm:1722) 11 HitAndRescue 0x000000010091510c TextRenderingPrivate::Font::AddCharacterToTexture(unsigned int, int, unsigned int) (Font.cpp:685) 12 HitAndRescue 0x000000010091564c TextRenderingPrivate::Font::CacheFontForText(unsigned short*, int, int, unsigned int, std::__1::vector<TextRenderingPrivate::TextFormatChange, std::__1::allocator<TextRenderingPrivate::TextFormatChange> >) (Font.cpp:827) 13 HitAndRescue 0x0000000100922c54 TextRenderingPrivate::NativeTextGenerator::Setup() (TextGenerator.cpp:208) 14 HitAndRescue 0x0000000100926db0 TextRenderingPrivate::TextMeshGenerator::Generate() (TextMeshGenerator.cpp:294) 15 HitAndRescue 0x0000000100926c0c TextRenderingPrivate::TextMeshGenerator::Get(UTF16String const&, TextRenderingPrivate::Font*, TextAnchor, TextAlignment, float, float, float, bool, bool, ColorRGBA32, int, int) (TextMeshGenerator.cpp:99) 16 HitAndRescue 0x0000000100911620 TextRenderingModule::TMGenGet(UTF16String const&, TextRendering::Font*, TextAnchor, TextAlignment, float, float, float, bool, bool, ColorRGBA32, int, int) const (TextRenderingModule.cpp:20) 17 HitAndRescue 0x0000000100654798 IMGUI::GetGenerator(RectT<float> const&, GUIContent const&, TextRendering::Font*, TextAnchor, bool, bool, ColorRGBA32, int, int, ImagePosition) (IMGUIUtils.cpp:77) 18 HitAndRescue 0x0000000100650db4 GUIStyle::GetGenerator(RectT<float> const&, GUIContent&) const (GUIStyle.cpp:598) 19 HitAndRescue 0x000000010065108c GUIStyle::CalcSize(GUIContent&) const (GUIStyle.cpp:435) 20 HitAndRescue 0x000000010095f604 GUIStyle_CUSTOM_Internal_CalcSize(void*, ScriptingObject*, Vector2fIcall*) (GUIStyleBindings.gen.cpp:660) 21 HitAndRescue 0x0000000100238490 GUIStyle_CalcSize_m2752 (Bulk_UnityEngine_0.cpp:17509) 22 HitAndRescue 0x0000000100066c10 GUIHelper_GetSuggestedFontSizeFull_m1719 (Bulk_Assembly-CSharp_0.cpp:33257) 23 HitAndRescue 0x00000001000a8f84 SignupScreen_InitLayoutVariable_m2399 (Bulk_Assembly-CSharp_1.cpp:23558) 24 HitAndRescue 0x00000001000a5e2c SignupScreen__ctor_m2394 (Bulk_Assembly-CSharp_1.cpp:23316) 25 HitAndRescue 0x00000001000a5b70 LoginScreen_Start_m2349 (Bulk_Assembly-CSharp_1.cpp:21572) 26 HitAndRescue 0x00000001003c2da4 RuntimeInvoker_Void_t189(MethodInfo const*, void*, void**) (GeneratedInvokers.cpp:12) 27 HitAndRescue 0x0000000100dd09e0 il2cpp::vm::Runtime::Invoke(MethodInfo const*, void*, void**, Il2CppObject**) (Runtime.cpp:299) 28 HitAndRescue 0x00000001006d4f24 ScriptingInvocation::Invoke(ScriptingException**, bool) (ScriptingInvocation.cpp:128) 29 HitAndRescue 0x00000001006cf1c4 MonoBehaviour::InvokeMethodOrCoroutineChecked(ScriptingMethodIl2Cpp, ScriptingObject*, ScriptingException**) (MonoBehaviour.cpp:844) 30 HitAndRescue 0x00000001006cf710 MonoBehaviour::InvokeMethodOrCoroutineChecked(ScriptingMethodIl2Cpp, ScriptingObject*) (MonoBehaviour.cpp:926) 31 HitAndRescue 0x00000001006ce6bc MonoBehaviour::DoGUI(MonoBehaviour::GUILayoutType, int) (MonoBehaviour.cpp:358) 32 HitAndRescue 0x000000010064cd64 GUIManager::DoGUIEvent(InputEvent&, bool) (GUIManager.cpp:315) 33 HitAndRescue 0x000000010064d2b4 GUIManager::SendQueuedEvents() (GUIManager.cpp:142) 34 HitAndRescue 0x0000000100683d68 PlayerLoop(bool, bool, IHookEvent*) (Player.cpp:1829) 35 HitAndRescue 0x0000000100487024 UnityPlayerLoopImpl(bool) (LibEntryPoint.mm:235) 36 HitAndRescue 0x000000010000b47c UnityRepaint (UnityAppController+Rendering.mm:246) 37 HitAndRescue 0x000000010000b2e0 __51-[UnityAppController(Rendering) repaintDisplayLink]_block_invoke (UnityAppController+Rendering.mm:52) 38 libdispatch.dylib 0x00000001963b5990 _dispatch_call_block_and_release + 20 39 libdispatch.dylib 0x00000001963b5950 _dispatch_client_callout + 12 40 libdispatch.dylib 0x00000001963ba208 _dispatch_main_queue_callback_4CF + 1604 41 CoreFoundation 0x000000018411f7f4 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 8 42 CoreFoundation 0x000000018411d89c __CFRunLoopRun + 1488 43 CoreFoundation 0x00000001840492d0 CFRunLoopRunSpecific + 392 44 GraphicsServices 0x000000018d9776f8 GSEventRunModal + 164 45 UIKit 0x0000000188c46f3c UIApplicationMain + 1484 46 HitAndRescue 0x00000001000055d0 main (main.mm:40) 47 libdyld.dylib 0x00000001963e2a04 start + 0
虽然并不能100%确定是这个原因造成的（待验证，验证后再来补充），但是保险起见，还是选ES2.0比较好。
另外Android不开多线程渲染之前说过的。