Well I've gone for Carry amount first up to 60 then I'll go for speed I guess - although it's sometimes quite nice to just trot through the scenery and appreciate it.
I go to 40 speed, then start adding stamina, cause I don't like getting knocked off the horse when trying to run past enemies. Carrying capacity is last, cause I can buy more inventory space (same thing) from a bag merchant
60 inventory -> 60 stamina -> 60 speed
But that was before I realized that a fully maxed mount was too fast once some random person cast rapids. Going that fast hurts my eyes. Newer characters follow the above but don't apply any points to speed at all (expect for any character bound speed boost books they may end up with).
PC-NA / PC-EU
ID @IsharaMeradin
Characters NA
Verin Jenet Eshava - Dark Elf Warden (main)
Nerissa Valin - Imperial Necromancer (secondary)
Lugsa-Lota-Stuph - Argonian Sorcerer
Leanne Martin - Breton Templar
Latash Gra-Ushaba - Orc Dragonknight
Ishara Merádin - Redguard Nightblade
Arylina Loreal - High Elf Sorcerer
Sasha al'Therin - Nord Necromancer
Paula Roseróbloom - Wood Elf Warden
Ja'Linga - Khajiit Arcanist
If you have ESO+, Personal Banker, Personal Merchant. Because you want to save time and hit all the landmarks as fast as possible. Having a banker and merchant reduces the need for a bigger inventory capacity.
I have been lvling 2 new toons after the resant speed nerf i have put over 30 points to get my mount to run faster than my toon and 4 points in stam to give me more stam my new toon. So to me a mount is worthless for over 30 days when a mount should have more speed and stam than a toon just saying. So 2 in speed and 1 in stam to 60 speed and then 2 in stam and 1 in inventory to 60 in less your a pvp and can get rappeds