Speed

I personally find 36-38 speed to be a good place to avoid a lot doubling. Others that frequent Tier 20 might say something different, however.

For the most part I would say 36/37.

(Damnit you beat me)

I'd say around 35 speed is a good speed to avoid doubles from a majority of the cast (like 90 % percent), course this isn't taking into account skills and buffs.

Most of my heroes are in the mid 40s and higher.
Unless armor or dragons, others most of the rest are around there.

ya like that dude said. 36-38 unbuffed is very respectable and should,for the most part, keep you out of harms way for all but speedy swords and bluetomes.

I sit from tier 18-20 depending on how hard I try to stay in tier 20. Up in tier 20 though id say 40+ is required.

Basically as the other two have stated for a specific range of speed, the best way to avoid being doubled, is to be the one who does the doubling.

However there are exceptions to this, such as Wary Fighter even though that is limited to only Armoured units.

Depends.

Unmerged not considering SI: 37 is the number I’d shoot for, because then literally the only units who can double you without any SI help are Ayra, Mia, Linde, and Lonqu, and only one of those sees a wide amount of use.

SI/buffs consideration: a minimum of 40 would be good to make it more likely you double and don’t get doubled.

Max merged without SI: At the minimum, 41 since you’re looking at a +4 to all stats with max merge.

With SI/buffs Max: baseline here should be about 45 before in combat skills, pushing closer to 50 during combat. A Nino with a max merge build can easily hit 50 speed with a single hone spd, Ayra can surpass 50 and go towards 55 during combat, and there are crazy builds for teams the run Amelia that can push her speed to 60, and LA Lyn has the potential to flirt with 80 speed.

In short, there is no such thing as too much speed.

To add to what a lot of people are saying already the mid 30s is a decent spot to be if we aren't talking hone buffs. But again it really does depend. Mostly it depends on what you want your unit to fight.

If we are talking a red unit, greens tend to be slower so you can get away with less speed. If it's a blue, reds can be blisteringly fast so it raises. Look at what you're targeting with a unit and ask what speed do they have? Then adjust accordingly.

As others have mentioned 36-38 is around a good number to avoid doubles as a rule of thumb, but you have to keep in mind that the value of speed diminishes as a stat at higher tiers due to the number of units that guarantee double through skills (QR, Bold/Vengeful Fighter) or prevent doubles (wary fighter, Myrrh), hence it becomes a relatively less valued stat for most of the units with decent bulk and middling speed. Only units where I'd be desperate for a +spd variant these days would be fast sword users like Ayra or glass cannon mages