> The incredibly aggressive people that you're talking about is mostly floor traders, brokers, etc, because they need to be that way, and they're generally on their way out, as algos will be smarter and faster.

This is definitely true but they're not always aggressive. Generally quants are the nicest people I've had to work with in the industry. I've had a floor trader kick me hard under his desk because I wasn't replacing his Bloomberg keyboard fast enough (<2 minutes). That's said, I've have a quant or two be a passive-aggressive dickwad too...but in general, way nicer than floor traders.

Would you say that, as a HFT shop, you are only competing with other HFT shops? I've heard that HFTs use nearly identical algorithms, so now its basically a competition for real estate near the exchanges.

Real estate near exchanges has essentially been standardized and is no longer a significant strategic advantage.

HFT shops compete for real estate and hiring (especially this and fiercely - non-complete clauses and lawsuits are standard) with each other but in terms of their trading competition it varies widely based on what algos they use.

An algo is basically just a trading strategy (sure, there's a basic set of these) but speed of data collection/processing and execution gives you more options. You can design an algo to hunt other HFTs or not. You can also trade against HFTs if you're not.