It costs 1TB to sell 600 units of an item (regardless of value - 1, 2, or 3 coins) - so this will net you a maximum of 1800 coins per TB if you are selling the top value item.
Option 1: The cheapest option is the exchange of 1 Tower Bux for 250
coins. Let's represent the words "Tower Bux" as "TB" in an effort to
save time. 250 coins / 1TB = 250 coins. Therefore, 1TB= 250 coins in
the first option. It's an OK investment, but as a persistent investor,
you can find a better option.
Option 2: The second option is the exchange of 5 Tower Bux for 1,500
coins. That would mean that 1 Tower Bux, or 1TB, equals 300 coins.
1,500 coins / 5TB = 300 coins, therefore 1TB = 300 coins. The second
option would seem to be the better investment, because in Option 2,
one Bux equals a whole 50 coins more than in Option 1.
Option 3: Now let's move on to Option 3, which is the exchange of 20
Tower Bux for 20,000 coins. If I do the math; 20,000 coins / 20TB =
1,000 coins, therefore 1TB = 1,000 coins. Huge difference, right?
That shoots the worth of a Tower Bux up from 300 coins to 1,000 coins,
making Option 3 the best investment so far.
Option 4: This final and most costly exchange is 50 Tower Bux for
100,000 coins. Here's the math: 100,000 coins / 50TB = 2,000 TB.
Therefore, 1TB equals a whopping 2,000 coins, which would be the
obvious best investment. Considering that the original value of a
Tower Bux was 250 coins and now it's 2,000 coins, the final value of
one Tower Bux is 8 TIMES MORE than the original investment!
The profit per upgrade is 765 coins/ stock-sale cycle with all 3 dream
jobs filled. It's roughly 8 stock-sell cycles,
which for most floors will take under 1 day each cycle (at best), or
a week to 8 days (at worst) to be making extra compared to buying
coins. It would appear to be a good investment to upgrade floors,
especially where you have dream jobbers for that floor.
Each upgrade of a floor costs you 3 TB, so you gain roughly 255 coins/sale cycle per TB spent.
If you want fast money, saving TB and taking them to the bank nets you the most bang for your TB instantly, if you save to the top-level of a 50 TB trade. Upgrading floors is probably your second best bet, if you want more money over time. Quick selling is good for a quick cash infusion.
Best Answer
You can get Bux by:
The easiest way to get lots of bux, if you have a large number of residential/commercial floors, is to evict bitizens that don't have their dream job and pay Bux to get new bitizens to replace them. If you have the majority of different floor types, more often than not these bitizens will be able to give you 2 bux, netting 1 bux after losing one to instantly move in the new bitizen. Even if you have all skill level 9 employees in their dream job, you can still swap out one of your level 9 employees for the new one and then immediately put the first one back again, evicting the inferior employee, but still getting your 2 bux for giving them their dream job. In this way you can slowly but steadily accumulate bux, as long as you have empty apartment slots to move bitizens into. This is why the wiki recommends keeping as many residential floors as possible with only four residents, as any bitizen who arrives at a floor with vacancies will move in and save you the one bux you would otherwise pay to move someone in.