tl;dr go grind some low tiers, at least up untill you have all tier 4 tanks, maybe more.
Say you wanted to unlock the whole tech tree as fast as possible, one of the quickest way to do so would be with blueprints and the daily missions can help a lot there. According to this post and my own maths, the expected value of the daily missions is 2.083 blueprints per day, assuming you do all the missions. This can go up to 2.15 BP per day if you use your reroll correctly, which means rerolling the highest mission without BP.
However, those BP can drop up and down the tech tree. I have found that lately, they tend to drop at the lowest tank you haven’t unlocked, but this may be biased. Now, obviously, you want those BP to drop on the fat tier 10 tanks, because that saves you the most XP. How much XP? Let’s take a look in this overview, which lists tiers, the BP you need to unlock a tank of that tier, the average XP tanks cost to research at that tier, the average XP you save by gaining a BP, and this value multiplied by the 2.083 expected value and the reroll expected value.
Tier BP XP XP per BP Daily value (XP) Reroll value (XP) 2 4 263 66 137 4 3 4 1325 331 690 23 4 4 3916 979 2039 67 5 6 13105 2184 4550 149 6 6 29697 4950 10310 339 7 8 67772 8471 17646 580 8 8 95621 11953 24897 818 9 10 164029 16403 34167 1123 10 12 223539 18628 38803 1275
What we can see here, is that playing daily massively increases your BP rewards and the XP that comes from that. However, if you can make the BP drop at higher tiers, this also gives you a massive increase. Unlocking all tier four tanks, for example, ”only” costs about 140K XP, but it increases the average daily XP value of your blueprints from roughly 14K to 21K (assuming a fair distribution, which I’m not seeing). That’s a 7K increase, so you’d need about 140/7=20 BP to ”break even”. With an expected 2 BP per day, that is only 10 days of playing your missions! When you get up the trees far and wide, this wierdly speeds up your progress in the depth as well.
I have used this method of rerolls to really snowball my progress: right now, I have all tanks up to tier 9 blueprinted and have 6/12 BP for all tier 10s, some more. It’s extremely satisfying to get a 5x BP mission now because it’s the equivalent of a 90K XP drop to me. There is one big downside to this BP method though: stock grinds. Identify where you want to use your free XP, because some tanks suck more than others when stock. Also note that the rerolls aren’t really worth it in my personal opinion, because a 1250 free XP mission is worth more to me than the 1275 (or less) fixed XP, especially given the stock grind issue.