Learn / Experienced · Chain Library

Choosing a chain for a job

Beginners often ask “which chain is best?” Experienced users ask a better question: best for what? A chain that is excellent for settling large transfers may be clumsy for small, frequent payments, and the reverse. This module gives you a way to compare chains by the job you need done.

We use Bitcoin, Ethereum, Solana and Ethereum’s layer 2 networks as examples, in line with the History lessons, and we deliberately leave out prices.

Education only, not financial advice. Examples use made-up numbers, not live prices.

Layer 1 and layer 2 in one minute

A layer 1 is a base blockchain with its own validators and security, such as Bitcoin, Ethereum or Solana. A layer 2 is a separate network built on top of a layer 1. Its aim is to do the busy work of processing transactions more cheaply, then lean on the layer 1 for final security.

Think of a layer 1 as a courthouse and a layer 2 as a busy local office that does most of the paperwork and files a summary with the courthouse. The local office is faster, but you rely on it staying honest and on the courthouse being able to check.

How rollups work

The most common kind of layer 2 on Ethereum is the rollup. It bundles many transactions, processes them off the main chain, and posts compressed data back to Ethereum. Examples named in Ethereum’s own documentation include Arbitrum, Optimism and Base. There are two main designs:

• Optimistic rollups assume a batch is valid unless someone proves otherwise. Withdrawals to Ethereum usually wait for a challenge period of about seven days, so anyone watching can raise a fraud proof.
• ZK rollups attach a mathematical validity proof to each batch, so there is no long challenge window. They are more complex to build and run.

Why fees fell

In March 2024 Ethereum’s Dencun upgrade introduced “blobs”, a cheaper lane of temporary data space designed for rollups. Because rollups pay less to post their data, they could pass lower fees to users. Fees still change with demand, so treat any fee you read as a snapshot, not a promise.

The hidden cost: moving between chains

Using a layer 2 means your funds sit on that network. To get back to Ethereum you either wait out the withdrawal period or pay a third-party “bridge” to front the money for a fee. Bridges are separate programs with their own risks. Module 5 explains how some of the largest crypto thefts happened on bridges, so when you can, avoid moving funds between chains more often than you need to.

A simple way to compare

Before choosing a chain, write down the job and score each candidate on five questions:

• Security: who secures it, and how many independent validators are there?
• Cost: what does a typical transaction cost at a quiet time and at a busy time?
• Speed and finality: how long until a transaction is practically final, and how long to get money out?
• Ecosystem: are the wallets, apps and exchanges you need actually available?
• Track record: has it had outages, exploits or rule changes, and how were they handled?

Speed claims need context

You will see “transactions per second” figures. They are not directly comparable. As rough, commonly quoted ideas, Bitcoin handles several transactions per second and Ethereum’s base layer around fifteen, while some other chains advertise thousands. Peak lab numbers, real everyday use and what counts as one transaction all differ. Solana, for example, has had periods when the network stalled, which is a reminder to read the track record as well as the headline.

A Caribbean angle

For someone sending small amounts to family overseas, low fees and a quick, simple way to get money out matter more than technical bragging rights. For someone holding savings long term, security and a long track record matter more than speed. The same person can reasonably use different chains for different jobs. Whatever you choose, check what exchanges and wallets available to you support, and read the rules lesson (E8) before moving money.

Worked example: a small monthly transfer

Suppose you want to send a modest amount to a relative abroad every month. Start with the job: the amount is small, the timing is flexible, and the receiver needs to turn it into local money easily. That points you to the questions of cost and exit, not to speed records.

Write the steps out. You buy a coin on an exchange, send it on a chain, and the receiver sells it on their own exchange. Each step has a fee and each exchange supports only certain chains. If the receiver’s exchange does not accept a layer 2, using it would force a bridge or an extra withdrawal, which adds cost and risk. A chain that looks cheap on paper may be the most expensive in practice.

Now compare two candidates. Chain A is a well-known layer 1 with higher fees but wide exchange support. Chain B is a layer 2 with low fees but fewer exchanges. For a monthly transfer, check what each exchange charges to withdraw on that chain, not just the network fee. Also test with a tiny amount first. The point of this exercise is to see that the “best” chain is the one that works for both ends of the journey.

Common mistakes

Chasing the lowest fee. A cheap chain with weak security or little support can cost far more if something goes wrong.

Forgetting the exit. Check how and how fast you can get funds out before you put them in.

Bridging for fun. Every bridge is extra risk. Move only what and when you must.

Treating speed numbers as a ranking. Different counting methods make them hard to compare.

Try it yourself

Pick a real job, such as “send a small amount to a relative every month”, and two chains that could do it. Fill in the five questions for each using official documentation, not social media. Then write one sentence: what would make you pick the other chain?

Keep in mind

• Choose a chain for a job, not a reputation.
• Layer 2s lower costs but add their own trust and exit risks.
• Fees and speeds change; read them as snapshots.
• Not financial advice.

Key terms from this lesson

• Layer 1 — a base blockchain with its own security.
• Layer 2 — a network built on a layer 1 to make use cheaper and faster.
• Rollup — a layer 2 that bundles transactions and posts data to the layer 1.
• Challenge period — the waiting time in which an optimistic rollup batch can be disputed.
• Blob — temporary data space on Ethereum used mainly by rollups.
• Bridge — a program that moves value between chains.

Sources and credits

• ethereum.org: Layer 2 scaling — official overview of layer 2s
• ethereum.org: Optimistic rollups — challenge periods and fraud proofs
• ethereum.org: Zero-knowledge rollups — validity proofs
• Spark glossary: Optimistic rollup — about seven-day challenge period and blob changes after Dencun
• ethereum.org: Gas and fees — why fees change with demand

Explained in our own words from these sources. Figures are approximate and reported by the sources named; check them yourself. Education only, not financial advice.

Module quiz

3 questions. Tap an answer to see if you are right and why. Get 2 right to complete the module.

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