I'm of the opinion that burst draw spells and draw engines aren't really directly comparable. They each have their upsides and downsides.
There have definitely been games where I've played a Phyrexian Arena on turn three and the steady influx of additional cards it has given me throughout the game has made the difference between me winning and losing.
There are probably an equal number of games where I've drawn Arena late game and wished it was a burst "draw two" spell instead.
Ultimately I think it comes down to your meta and the kinds of games you usually play. If your group likes to play long battle cruiser style games that regularly go past turn 10 or so, the engines are great. If your games tend to be a little faster and more active, then burst spells are good. Both styles and strategies are good in the right place and bad in the wrong place. You just have to be able to tell which is which.
As for these specific burst spells, they're all good. My favourites are Sign in Blood and Read the Bones, but that's because I play a lot of mono black or heavy black decks.
Sign in Blood being able to target any player is occasionally relevant so if you can handle the double black cost it's worth it over Night's Whisper. Read the bones can dig you a little deeper which I personally feel is worth the extra mana over whisper too. That said, I'll still gladly run whisper too, but for me personally I'd include the others first.
Painful Truths is probably the one I'm least hot for. Still decent enough if you're in 3 colours and one of them isn't blue though.
This pretty much sums up my takeaway from the responses on this discussion.
I like having immediate draw like the spells we are talking about
and having draw engines because they fulfill separate roles. To me, immediate draw is good in "emergencies" when you need a land, removal spell, etc. because their cost efficiency is so high. They're good for getting you set up with the cards you need and you don't need to
jump through any hoops to use these spells.
Engines are good to keep you going and allow you to further your boardstate without being susceptible to a wipe. If you aren't already set up with whatever gameplan your deck employs already running, it's likely that the draw engine will either do nothing or do very little (
Phyrexian Arena is the exception, but that card is just nuts in so many ways). They're win more cards.
I think that after what I've seen, I like
Read the Bones the most (in multicolor decks). I think that it's very dependent on the curve of your deck, as if you have a bunch of 3 drops,
Night's Whisper/
Sign in Blood might be better so you don't have another 3 drop
and Read the Bones stuck in your hand, but otherwise, I like it better. You basically pay an additional mana of any color to scry 2, which I think is worth.
I see what you're saying about
Sign in Blood, but I include draw spells like these for situations where things aren't going according to plan, whether that means I'm not drawing enough lands/the right type of lands or I'm being hated out and am running low on cards. If my mana isn't right, then I just might not have the double black mana necessary to cast
Sign in Blood, which defeats the reason why I included it in the first place.
Painful Truths can definitely be good, but I'm still of the opinion that quick draw spells are good at bailing you out of awkward situations and if you have 3 colors to get full value out of
Painful Truths, then you aren't desperate for it. If you only have 2, it's worse than all the other spells we've mentioned. If you are including it because you have a really good mana base & can consistently hit 3+ colors and want a 3 mana draw 3 spell at any point in the game, then I think it can easily be one of the best if not the best of the 4 we've talked about.