I bought a case of screwtop glass bottles that I use, for the most part. Similar to these, except that the ones I got were round. Pretty sure I got the ones I did because they were cheapest; if I ever need to add more, I'll probably get swingtops, because there is noting more irritating that a syrup bottle whose cap is dried shut. I literally have an old pair of Channellock pliers in my bar to wrench them off.

I also reuse bottles that have nice labels (as in, don't come off) for their respective syrups: homemade cinnamon, grenadine, and vanilla syrups now inhabit 375ml bottles of the same from BG Reynolds, and I have 750ml orgeat and passion fruit syrup bottles from Liquid Alchemist that get refilled with homemade versions. Though, their orgeat is still miles ahead of mine :/

I always recommend these. Good 8.5 oz size. Square shape so you can fit them better in the fridge. Boil to sterilize. Just write the syrup name and made date on the glass with a Sharpie, and it washes off. https://www.amazon.com/Clear-Glass-Quadra-Bottles-250ml/dp/B00P1KC27S/ref=sr_1_4