I ended up weighting fill quality over the advertised raw spread. On one trial account the spread looked half a pip tighter, but rejections on EURUSD market orders at London open made the effective cost worse than the slightly wider book I use now.
Moving the VPS into the same city as the broker cut round trip enough that my usual limit entries started filling on the first touch instead of chasing. That gain showed up in the fill log within a week.
The scalping clause in the terms is the one I actually read line by line. A broker that reserved the right to cancel sub-minute trades was an immediate no, regardless of the platform.
Withdrawals were the last filter. Two small live tests and a same-week payout request beat any demo comparison I had run.
Which of those filters would you drop first if you could only keep three? For me the terms and fill logs stay, and the marketing page never enters the shortlist.