This is probably way more answers than you wanted, haha, but here goes... (source: I'm a lawyer and I help create mutual funds and ETFs)
Taxes:
Because ETF shares are traded on the secondary market, rather than directly at the Fund level, the actual Fund can have less turnover in securities. Additionally, any shares that are traded directly with the Fund (called creation units, which are large blocks of shares traded by institutions) are often traded 'in-kind' which means that the shares are traded for securities held by the Fund, rather than cash. That means the Fund doesn't have to go out and by and sell securities as people come and go from the Fund (so another way to achieve less turnover). Low turnover = lower capital gains.
I'll note that you still have to pay capital gains taxes on increases in the value of the shares you own, when you sell those shares.
Personally, I don't think this (tax benefits) is a huge enough factor to make a decision off of, but I don't have any math to prove it.
One other note is that many Vanguard ETFs are share classes of their mutual funds, which means that the tax benefits are balanced across the whole Fund (mutual fund classes and ETF classes). They just push out any of their low basis securities through the ETF in-kind redemption process. So in a "share class ETF" there's no difference in the tax benefits for the ETF class vs the mutual fund class.
One MORE note. Many fixed-income ETFs don't do redemption in-kind just because its harder for them to trade pieces of bonds with institutions, as opposed to equities which are typically more liquid and easily divided into small pieces. I don't know off the top of my head if Vanguard's bond ETFs trade in-kind.
Mutual Funds vs ETFs:
ETFs are almost always better, but that's solely because of the lower fees. There's no "magic" to ETFs, so if you see a mutual fund that you like and it turns out to be cheaper than a comparable ETF, by all means go with the mutual fund. It's not a trick. I could go into a lot of detail about why ETFs are cheaper but it boils down to how much work it is to maintain your mutual fund account, and how the industry has just evolved differently and brokers don't expect to receive as much payment for selling ETFs to their customers.
ETFs do have some disadvantages to mutual funds as far as ease of use. Particularly for people who want have a systematic deposit into their account. ETFs are more DIY (part of why they are cheaper), so while with a mutual fund you can set up an arrangement with the mutual fund company where they take a certain amount of money from you on a set schedule and buy mutual fund shares for you, you typically have to go out and buy your own ETF shares in your brokerage account (so if you wanted to do it weekly, you would have to buy shares every week).
The fractional shares issue is actually the reason why ETF companies can't set up systematic purchases. There is a way to get around this--the broker can buy full shares in their proprietary (like personal) account, and then credit pieces of the shares to different customers, and I understand there are brokers that do this, but I don't know which ones.
There's also the issue of commissions. If, you are buying the ETFs commission-free (for example Schwab's OneSource platform) then you don't have to worry about this. But if you are paying commissions on trades and buy a few shares weekly that is really going to add up. Don't do that. Either find commission free ETFs or go with a mutual fund. If you buy direct from Vanguard, that's commission free.
Personally, I think the cost savings on an ETF are worth the effort of doing your own trading. But I only transfer money from my bank to my brokerage account every month or so when a large enough pile of money has built up. ;) Maybe you would want to reduce the frequencies of your systematic purchases to ease the burden? I know you lose out on market exposure a bit, I'm just not that concerned about that since I look at my bank account as kind of an emergency fund (I mean, how do people decide their emergency fund should be $10k vs $11k?)
This comparison was mainly about costs vs ease of use, but I would be remiss not to note that another benefit of ETFs is the ability to trade intra-day (if you are strongly opposed to market timing, this should not matter much to you I suppose), and another benefit of mutual funds is that the price always exactly reflects what the Fund holds (ETFs are sold at market prices, so can be different form the actual value, but there are mechanisms that keep it really close, so not a big deal).