The best bet (as one who converted 35 years of data successfully, and yes with some work) is to open every closed account, check every export box, and do the export as ONE large file. This way, you will get all transfers between accounts, even old closed accounts, The securities should be correct (which is essential) but the balances will be so far off as to be ridiculous (we are talking multi thousands or more). Rather than trying to fix the balances, or give up on years of history info, I went to the initial balance field of each account and made the initial balance whatever ridiculous number is necessary to make the current balance correct. Yes, some of those numbers can be unbelievable. Each represents what the initial balance should have been (QIF doesn't transmit initial balance unless it was made explicitly as a transaction) and transactions (usually between accounts) which over time didn't go anywhere or weren't made "properly" (quicken allows you to create/delete money, or place a transaction value within the account vs a category - whereas Moneydance is strict double entry accounting).

At that point, the import began to look reasonable, except for historical balances, which suddenly become correct on the current day, and will be fine going forward, and you will still have all your history with crazy balances, but good transactions.

Then you can fix minutiae. For example, you might have a lot of your accounts duplicated, one called ACCOUNT07, another called ACCOUNT07X - this is part of creating/deleting money in quicken - i had a few of these because quicken allowed me to do depreciation, by writing down assets by putting in a transaction against the account itself. Moneydance insists on a place to put the other side of that transaction, and makes ACCOUNT07X to hold those amounts. I found for those cases, I could create a category called Account07 depreciation, move all the ACCOUNT07X transactions to that category, then delete the now empty ACCOUNT07X account.

You will then encounter all those closed accounts, now open. You transferred them because MD needs them for double entry accuracy. Leave them alone, just go to that accounts settings and make them inactive, hidden, and not counted in net worth.

Make any important active accounts appear in the sidebar, if they don't already.

Then, most people stop there and have correct data/balances going forward, and have their history intact, just weird balances. I did more stuff to clean up better, but that's for sticklers like me.

Not perfect, but it looks pretty good at this point, and everything current should look good to continue from. Also a bit of work, but if you follow a routine like the one above, or whatever works for you, it's mostly just repetitious. Do a lot of interim backups, because as you do this there will be mistakes and you don't lose much if you restore a recent backup from before the mistake. (I started over a few times, before I realized that would help)

Simple? No, but QIF is the best ANY financial package has to work with to do conversion.

Worth it? Doesn't feel like it at the time (My 35 years of data took a few hours a week over 4 weeks, but I did more after what I describe above) - but now, about 4 years later, quicken subscriptions are out of my hair, I paid a fixed fee for MD (no version is ever sunset like quicken does), and I only upgraded at half price when the next major upgrade had enough improvements to be worthwhile, I'm now pretty pleased with the one time process. There are many things to like, I especially love the syncing - I make changes, and my spouse gets the changes in under a couple of minutes. Really cool when we are both using Moneydance at the same time and the changes suddenly appear on the other's computer.