The newest version of E&P makes some major changes to the Alchemy Lab. In particular, the production times and costs have changed (mostly lowered across the board, making both higher-level recipes and alkashards in general much more accessible. In addition, the alkashard combine option has been modified to make emblem production a much more attractive option.
This guide uses the costs, times, and rewards from the beta beat: 
Early Information on "IMPROVED" Alchemy Lab [Part of The Beta Beat v30], as well as observations made since then, such as recipe 1B being more expensive than in the Beta. Thanks to @zephyr1 for all their hard work documenting and presenting all of this information. Also thanks to @Druid for his post below regarding crafting/ascension material use over time; I hadn’t actually anticipated this being an issue, and knowing that it absolutely is changes my recommendations a bit.
The big cuts to costs and times make the new Alchemy Lab a very interesting deal, especially for F2P and C2P players, as it opens a new avenue to farm emblems, and previously un-farmable 3-star and 4-star ascension mats. With that in mind, here is a quick analysis on what is and is not worth your time and investment.
- The cheapest in terms of food is 1B: 500 food per shard, 2 shards per hour. Efficient farmers will have that running 24/7; it’s the TC11 of the Alchemy Lab. EDIT 6/22/20: It has been brought to our attention that AL 1B has been boosted in price to 1800 food, which brings 1B’s efficiency down to 900 food per shard. Still nearly twice as good as any other level, but less useful than before. Also, as mentioned in @Druid’s post this recipe burns through 1-star crafting materials at a far higher rate than most people acquire them, so it’ll probably be necessary to alternate between this and another recipe.
- In terms of efficiency there’s a sort of sweet spot at 4B, 5B and 6B: roughly 1k food per shard, 2.5-2.7 shards per hour.
- It’s important to note that 5B also costs the Iron needed to craft the uncommon battle items in the first place: 7 bear banners costs 40530 iron (since I’m assuming you’re going to throw bear banners into this rather than something more expensive). It does, however, output a 3* battle item which is either more expensive or costs food to produce, so frankly that’s pretty much a wash; no one is substantively short on iron in the late game anyway, and being able to effectively purchase Revive scrolls and Super Antidotes using iron is a pretty good deal. Crafting material burn rate is going to be a problem with this recipe as well; in particular this recipe burns through 10 Metal Ores per day, which is more than most people earn through regular play. Farming S1-P15 and S2-P3/11 is recommended.
- Levels 7 and 8 have a big drop in efficiency for not much shard gain. 8B is also less interesting than 5B, because to feed it you need to sacrifice 5 Bomb attacks for 169K iron, which is a fairly significant sum even if iron is easier to come by than food in the late game.
- Level 9A bumps up to 3.1 shards per hour, but at more than double the food cost of 2.7k food per shard. Only take this if you literally have nothing better to do with your food (yeah, right!)
- 10A costs roughly 14 gems per day, which you can get at F2P if you’re lucky but is probably unsustainable without regularly putting cash in. On the other hand it’s a massively more efficient 6.25 shards per hour and costs only 119 food per shard, so in that sense you get what you pay for.
- 10B is a definitely unsustainable 28.5 gem per day burn rate, but also produces 6.25 shards per hour and costs only 214 food per shard.
Bottom line (Edited 6/22/20 for clarity): for F2P / C2P players I’d recommend loading up on 5B, both for the item generation and the alkashards, plus some combination of either 1B, 4B, 6B, and 10A as appropriate. 4B, 5B and 6B are the best balance of value-for-time-and-food; 1B is cheaper but slightly slower, and 10A is much faster at generating shards but costs gems so isn’t really appropriate for F2P. Also keep in mind that 1B and 5B are going to be limited in terms of the number of crafting materials that people receive: 1B burns through 144 1-star ingredients per day, and 5B burns through 10 metal ores, 5 crystal shards, and 5 mushrooms per day for bear banners.
This should net you roughly 1 pull at the alkashard lottery every 6 days or so when not spending gems, or roughly twice a week when throwing gems into 10A/B, at a cost of roughly 10% of your food production (7.2k food per hour) if you’ve maxed all your farms, advanced farms, and Watchtower.
