Depends on what you want to achieve.
> 0º equates to straight A-B, producing the maximum forward-facing direct-sound bias in the presence range and up. I'm set up for but never played much with that, except on my center omni when I was doing the "Decca Diamond" setup - in which case the center ball-mounted omni was always 0º.
> 45º is what I use, which adds some left/right stereo difference across that HF range which is welcome with A-B omnis IMO, and retains much of the forward bias. That's what I chose to use for Left/Right in combination with the center omni in search of more stereo info, but didn't dare to go wider angled at that time. Something of a safe medium.
> 90º will maximize the left/right stereo difference. I suspect especially useful for narrower spacings, and/or when center mics are used in combination, and gives up the forward biasing. I'm no longer scared of going wider angled as I was back then, especially when there is a center mic or pair in combination.
With my 6 channel setup I now actually orient them so the 45º angle faces backwards. That's because in this setup they are contributing ambience and low frequency pickup and pointing towards the back corners of the room provides a bit more HF differentiation between the forward and side-facing center mics. I want their "presence" focus to be on the room ambience and audience reaction rather than the direct sound from in front.
Of course, using a sphere (or plate) attachment eliminates the "near-perfect omniness" of The miniature DPA omnis which is a characteristic of their extremely small size, replacing it with a form of limited range controlled directivity along with the modification in timbre. That "near-perfect" omniness and flatter response is many times a positive attribute in itself.
Options are good.