In my experience, finding that perfect balance is basically impossible but i think the Sigma 18-50mm f/2.8 DC DN Contemporary for Sony E is your best bet for travel. I used it on my Sony a6700 and honestly it's so tiny that it makes the setup feel way less bulky for street photography. But yeah, be careful because it doesnt have built-in stabilization. If your doing handheld work on the Sony FX30, the Tamron 17-70mm f/2.8 Di III-A VC RXD for Sony E is probably better because of the VC, but man is it heavy... I found it kinda threw off the balance on small gimbals. The Sony E 16-55mm f/2.8 G is highkey the sharpest, but basically twice the price. I would suggest the Sigma unless you really need that 70mm reach... just use gyro data for stabilization later lol

honestly id grab the Tamron 17-70mm f/2.8 Di III-A VC RXD.

• $700 price point
• Awesome VC stabilization Works great for vlogging on the Sony FX30 Cinema Line Camera!

Saw this post a few hours ago and it really got me thinking about the reliability of these setups. Reminds me of my buddy Dave who was obsessed with finding the ultimate travel lens for his rig. We were trekking through this tiny town in the mountains, and he was so paralyzed by whether he should use his big heavy zoom or the small pancake lens he brought that he literally missed the most epic shot. There was this old monk walking through a beam of light, totally cinematic, and Dave was just standing there with his bag open, switching back and forth, muttering about constant apertures and barrel distortion. By the time he actually clicked the shutter, the guy was gone and the light had shifted. It turned into this whole ordeal where he spent the rest of the night looking through his gear bag instead of enjoying the local food. I think he eventually just sold half his kit out of frustration when we got home. Man, those gear dilemmas can really eat you alive if you let them...

yo, i actually went through this exact same dilemma a few months ago when i was prepping for a trip with my a6700 and fx30 setup. i originally tried to stick with just primes, but like you said, run-and-gun street photography and vlogging really demand a solid zoom lens. honestly, it was such a headache trying to swap lenses in the middle of a busy street lol. after testing them out, i'm highkey gonna recommend the Tamron 17-70mm f/2.8 Di III-A VC RXD for your specific use case. i know the weight seems like a lot compared to that tiny sigma, but since you're shooting on the Sony FX30 Digital Cinema Camera and the Sony a6700 Mirrorless Camera, having the built-in vibration compensation (VC) in the lens is a total game changer for handheld video. the fx30 ibis is pretty good, but combining it with the tamron's stabilization makes for much smoother footage without needing a gimbal every five minutes. here's why i think it beats the others for a two-body setup:

• the Tamron 17-70mm f/2.8 Di III-A VC RXD has optical stabilization which helps way more than you'd think for video.
• the extra reach up to 70mm is huge because when you shoot 4k60 on the fx30, there's a slight crop that makes the 50mm on the sigma feel a bit short for detail shots.
• the Sony E 16-55mm f/2.8 G is technically the sharpest, but it's expensive and lacks stabilization. i guess the lesson i learned is that while weight matters, for video work, having that extra stabilization and focal range is worth the extra few ounces in my bag. i've been pretty happy with the results and have no complaints about the image quality on either body. hope that helps! peace

Regarding what #4 said about "Saw this post a few hours ago and..." - that story about Dave is a total mood. Seriously dont be that guy who misses the shot because he is overthinking the gear lol. It seems like the thread is basically split between the tiny Sigma for portability and the Tamron for the extra features. Both are decent options depending on your needs but honestly just check YouTube. Theres a great video about this exact comparison, just search for a6700 fx30 zoom lens shootout and its like the first result. It shows the autofocus and stabilization in real time which is way more helpful than us just typing about it. I saw a really good breakdown there last week that basically answers everything you're asking about the low light performance and sharpness. Check it out!