Ok, but even in your scenario (assuming a Harmonized Samara Tree) you'd still need to wait 4 turns in order to get the full 3 mana (4 mana off the price of whatever you cast -1 for the mana you spent when Samara Tree casted the pod in the first place). Even then that's only 1 more mana saved than if you had casted it from the Vine Tree and you don't need to wait 4 turns for it then. Now I get that there's probably something I'm missing here, but what is it? Perhaps I'm underestimating the Seedling Pods.
Yes in a one round comparison vine tree will generally be > Samara.
Extrapolate that into a game wide effect and it can look something like this.
Druid cast a Samara tree.
Next turn Samara tree casts a seed pod A.
Next turn Samara casts pod B. A is at 1.
Next turn Samara casts pod C. Pod A is at 2, pod B is at 1 mana.
Next turn Pod A becomes anything you want it to be, Samara tree remakes pod A, Pod B is at 2, Pod C is at 1.
This cycle never ends. The Samara tree lets you spend 2 mana to get 3 in a few rounds, and that 3 mana is 100% versatile.
Also one of the biggest things to note here is that all of those pods, and subsequent actions, are a byproduct of the tree. The druid spent ZERO actions to make the pods. The only action was placing the tree. Free mana and free actions. I know Vine tree is more appealing but Samara has always been my favorite tree in this set. The sleeper hit IMO.
Alright, so (assuming Samara on turn 1) on turn 5 your tree will start "generating" a net of one mana for you per turn (2 if you harmonize the Samara on turn 1 as well). With the Vine Tree you start generating 1 (or 2 mana if Harmonized) on turn 2 with no wait time at all. Samara tree doesn't give you a mana advantage over Vine Tree unless you're cycling at least 4 Pods (in which case you start seeing returns on turn 6). The main advantage I can see over Vine Tree in this case is that you can cast any plant out of the pods instead of just vines, though that card-pool looks a little thin (mana flower, trees, wall of thorns iirc). I'm just not seeing a 3 turn delay being worth that without beatdown falling out of favour in the meta. On the other hand, the Vine Tree can also give some extra utility (1 mana for an extra vine marker).
I suppose a secondary advantage could be to cause your opponent to spend actions on the pods, though I can think of better ways of delaying an opponent (tanglevine, bloodspine wall, etc). At the same time though, there is a slight disadvantage since your opponent knows in which spaces you can cast spells, and when.
So what do you do? Rush in to beat down the samara tree? That is a lot of mana and investment for a turn 1 decision. Kill the pods? Well they have cantrip so have fun. I can spend 2 mana to make you waste an action or two killing pods that come back next turn. An Etherian Life tree, which a pod can become, makes them all 7 health to boot.
Would rushing the Samara Tree (or Vine Tree) really be a bad thing? It's likely to have Treebond, so destroying it not only gets rid of a deployment ability, but lowers the Druid's life by 4, channeling by 1, and she also loses the benefit of Lifebond +2. Seems like pressing the attack against her and her lifebond tree quickly would be the way to go. This is the major problem I have with waiting until turn 5 to get a return on your investment with the Samara tree. Actually, on turn 5 (with no Harmonize on Samara) you've spend 8 on the tree and 8 more casting Pods. In the same amount of time you'd made 4 mana from Treebond and have 3 mana on a Pod you can spend. Even ignoring the cost of the Samara in the first place you're still down 1 mana. So in essence you've spent a 1 mana and 1 quick action turn 1 for 1 quick action on turn 5. (It's even worse if you harmonize; the mana difference is the same but now you've spent two actions to get 1 back.) In an attack, the Vine tree can start defending you from turn 2. (For comparison, on turn 5 a non-harmonized Vine Tree would cost 9 mana but generate 4 and give you an extra 4 from lifebond, net =-1 [or +8 from the Samara tree scenario]. Additionally it would have given you 3 more possible deployments.)
Of course, the longer you wait to deploy using the pods the more your mana returns increase...but the early tempo and mana costs for that plan seem like they would outweigh any benefit. And the loss of a 4+ mana Pod would be painful to your economy.
Pods not popping fast enough? Use a shift enchantment wand
Are you suggesting that one should spend additional actions and mana to boost the pods? O_o
As a playtester you have more knowledge of the other cards than I do, so there may be something there that increases the effectiveness of the Samara Tree/Seedling Pod (such as a tree that increases the channeling of all other living creatures and conjurations by 1), but with the information I have right now the Samara Tree/Seedling Pod strategy looks inferior to the Vine Tree strategy due to the loss in tempo, especially since it doesn't offer a mana benefit unless you trade even more tempo for it. I really do hope there is something else that boosts it though.