29g 1/2" into the delts is a shallow IM if you're not morbidly obese and as painless as subQ, Best of both worlds.
If you want to minimize discomfort and avoid scarring(to keep those sites useable as long as possible) spend some time to get a quality precision needle, which will be far sharper and with a smoother surface that will inflect less micro trauma on the tissue by tearing.
BD Eclipse series is ideal, no more expensive than the Chinese made crap on Amazon, and well worth the effort to acquire. It's makes more of a difference than you'd think just changing brands would. They feel like a gauge or two smaller than they actually are.