I definitely prefer $25s over $20s. Most of my cash games are played in the chip range of 1/5 with the occasional 25, and keeping the multiple at x5 all the way across is consistent, and matches standard casino cash check denominations.
I may be biased because of having "grown up" working in a casino. The only place where we didn't use $25s was at the Pai Gow Poker tables, which were littered $20s... but that was only because of the awkwardness of 5% bank commissions on $25 bets.
When cashing out, you can prove one stack of five chips, and use it as the basis to match off singles, and fives... a stack of singles is a five, a stack of fives is a twenty-five - each stack equaling the next denom. It makes my style of cashing out quicker. The only time you need to work off a four-stack is if someone has a lot of twenty-fives... and people have no trouble watching those closely. The 1's and 5's are where the errors happen, throwing off the bank.
In practice, pretty much nobody gets to cash-out time with a single 25 or a single 20 chip. It's pretty much always 27, or 23, or 18... So it's irrelevant that the 25 doesn't match a single treasury note. People who end up with $20 will give you five red and get a single treasury note. One-chip-one-bill just doesn't carry any water, for me.
And if someone buys in or re-buys for exactly $20, I would never buy them in with a single chip, anyway. You get reds and/or whites. To get the $20/$50 checks, you'd need to buy in with a $50 or a $100... and if you buy in for a $50, I can't do it with a single chip type. If I have $25 checks, I can bring in a $50 or a $100 easily. But again, even on a $50 buy-in, I'm more likely to give a half-barrel of reds than a pair of $25 checks.
I guess it comes down to this: in any game that allows a $20 re-buy, a $20 chip doesn't play. You need to break it, anyway.
So what do I do when all the lower-denoms are in play? Easy. I color up the big stack, first! For most people, it feels like a reward. (Except for that chip-hoarder trying to build a fort.) That puts lower-denoms back in the bank, and I can rebuy someone properly. Otherwise, the first thing they'd do at table is color someone up, anyway.
HOWEVER, now that I'm thinking about it... I'm planning to get a set of non-denominated plaques to use as the "top denom" in cash games. Depending on the game, the top will be different. In my $1/$2 NL game, the plaques will be $100. But in a micro-stakes game, I may well use the plaques as $20s, instead of $25s...