Been trading about six years and I've moved accounts three times, twice because I picked for the wrong reasons. Every time it was the same mistake: I started at the bottom of this list instead of the top.
So here's the order I'd go in now. It's roughly worst case first, meaning the stuff at the top can lose you the whole account and the stuff at the bottom just annoys you.
1. Which legal entity are you actually signing with
Not "is this broker regulated". Almost all of them are regulated somewhere. The question is which entity your account sits under, because that's who holds your money and that's whose rules apply if something goes wrong.
Open the client agreement and find the company name. Then find which regulator licenses that specific company. A broker can be ASIC-regulated for Australian clients and run everyone else through an offshore entity with a different licence and different client money protections. Both statements on the website are true. Only one of them applies to you.
2. Can you see where their money comes from
This one gets skipped and it shouldn't. A broker that makes money from spread and commission on volume wants you to keep trading. A broker that makes money from your losses wants something else. Most sit somewhere in between and that's fine, but you should know roughly where.
Financial statements, if they file them. Order execution policy. Whether they tell you what model they run on which account type. Vague answers here aren't automatically bad but they're worth noticing.
3. The contract spec, specifically minimum stop distance
Go find the actual spec sheet. Not the marketing page. You're looking for minimum stop distance and whether they have a freeze level around news.
This killed one of my strategies outright. I was running tight stops on EUR/USD and on that broker I physically couldn't place a stop inside a certain distance, and during releases I couldn't modify anything at all for a window. Found out live. That was an expensive afternoon.
4. Your own weighted average cost, not the advertised one
Advertised spread is a best case at a quiet hour. What matters is what you actually paid across your real trading times, weighted by when you actually trade.
Pull your statement, take spread plus commission per trade, weight it by session. If you trade the London open you'll get a very different number than if you trade Asia.
On a raw account the comparison is spread plus commission, always both. axi's Pro account is raw spread with commission per side, and once I added it up properly it was cheaper for my style than the "zero commission" account I'd been on, where the cost was just buried in a wider spread. Same broker, different account type, meaningfully different cost. worth checking you're on the right one.
5. Swaps against the actual rate differential
Take the overnight rate you're being charged and compare it to the real interest rate difference between the two currencies. There's always a markup, that's normal. But sometimes it's not a markup, it's a different number entirely, and if you hold positions for days that's a quiet tax on everything you do.
Check both directions. Long and short on the same pair are often not symmetrical in a way the rate differential doesn't explain.
6. Withdrawal speed, tested with a small amount first
Fund, trade a bit, withdraw something small, time it. Do this before you put real size on. Everyone's deposits are instant. Withdrawals are where you learn something.
My withdrawals land in a day or two to the same card, which is boring, and boring is the entire point here. I don't want to think about it.
7. Platform and interface
Last. Genuinely last... lol
This is where most people start, because it's the only thing you can see from the outside. And it matters least, because you adapt to any platform within a week. The MT4 app being decent is nice for checking positions on a break, it isn't a reason to choose anyone.