I would say bonds... so far so good, that may change. I wouldn't say penny stocks, because they may use buying and selling algorithms on any volume generating news in advance of your position, or if you are a big investor or institution, you may get front run.
Hahahahha, your not for real are you? You lot actually believe there is a market on this planet that is untouched by these vermin? muwahahhaha. Hilarious!
Vermin, how cruel. Scum is more like it. The Botswana rice patty futures are said to be hft free, but the spread is 20%. You are posting too soon after your last post. Try again in a few minutes. We slow it down so that we don't get attacked by hft bots.
anything that allows a computer to place orders will have automated players. That's - all exchange traded securities - fx spot/forwards/swaps - rates - anything on tradeweb, brokertec, bank's own servers, etc - other stuff I am missing. You need to look where a human adds value. That is in the physical commodity trading business IMO.
IMO you are confusing automated trading (i.e. using computers to trade "autonomously" based on algorithms, also called algorithmic trading) with HFT (high frequency trading, i.e. using computers to operate ultra fast). While they may sometimes overlap, they are different. The OP was asking about HFT; you answered a question he/she didn't ask about automated trading.
My understanding is that HFTs are swarming all over ETFs; something as liquid as SPY is manna from heaven for HFTs. What makes you think otherwise?