I am in EU which limits my options (no pun intended).
1. Degiro is sort of Robinhood counterpart, but it's more expensive, does not have (documented) API and lacks access to US exchanges (for options).
2. Interactive Brokers is a heavyweight that provides API and all the bells & whistles you could ask, but it clearly expects larger accounts. I have < $100k invested right now which makes their commissions rather expensive for daytrading and there is effectively no support from them (which they don't state clearly, but none of my queries have been answered by a human).
3. ChoiceTrade is available in EU as well, but they refused to provide me API access. Their commissions (for US options) are lower than IB (for < $100k accounts at least), but the service itself has shadier reputation.
I have tried all three of these and decided to use IB. They provide two types of API. I am using a simpler one - "TWS API". It is widely used, so there is plenty of documentation and libraries. Protocol is pretty archaic and you need to run GUI Java-based app which acts as a gateway between your code and their servers, but there are documented ways to hack it for running in headless mode and performance is fine for my use case, so I didn't bother looking any ways around it. Additionally there is a second API, which is using FIX protocol that's "industry standard", but I'm not working in fintech and am not familiar with it / didn't need it so far. My understanding is that you still need to run the same local Java app if going FIX route.
That said, assuming most people here are from US, I would recommend to try starting out with either 1) Alpaca.markets (free, but only supports trading stocks) or 2) TD Ameritrade (both stocks and options). Both have modern REST API that you would expect in 21st century. Might be too limiting for professionals and definitely isn't meant for HFT, but IMO they should be sufficient for people algotrading as a hobby.
I know that there are other services as well, some specifically targeted for algotraders and some people even use reverse-engineered Robinhood API, but I can't vouch for any of these.
1. Degiro is sort of Robinhood counterpart, but it's more expensive, does not have (documented) API and lacks access to US exchanges (for options).
2. Interactive Brokers is a heavyweight that provides API and all the bells & whistles you could ask, but it clearly expects larger accounts. I have < $100k invested right now which makes their commissions rather expensive for daytrading and there is effectively no support from them (which they don't state clearly, but none of my queries have been answered by a human).
3. ChoiceTrade is available in EU as well, but they refused to provide me API access. Their commissions (for US options) are lower than IB (for < $100k accounts at least), but the service itself has shadier reputation.
I have tried all three of these and decided to use IB. They provide two types of API. I am using a simpler one - "TWS API". It is widely used, so there is plenty of documentation and libraries. Protocol is pretty archaic and you need to run GUI Java-based app which acts as a gateway between your code and their servers, but there are documented ways to hack it for running in headless mode and performance is fine for my use case, so I didn't bother looking any ways around it. Additionally there is a second API, which is using FIX protocol that's "industry standard", but I'm not working in fintech and am not familiar with it / didn't need it so far. My understanding is that you still need to run the same local Java app if going FIX route.
That said, assuming most people here are from US, I would recommend to try starting out with either 1) Alpaca.markets (free, but only supports trading stocks) or 2) TD Ameritrade (both stocks and options). Both have modern REST API that you would expect in 21st century. Might be too limiting for professionals and definitely isn't meant for HFT, but IMO they should be sufficient for people algotrading as a hobby.
I know that there are other services as well, some specifically targeted for algotraders and some people even use reverse-engineered Robinhood API, but I can't vouch for any of these.