How much of a disadvantage do I have if I don't use a poker HUD?
What benefits are there and which HUD's are the best ones?
How much disadvantage? playing one or two tables, not much. If we are talking about 3+ tables then pretty big unless you have the good memory in tracking everything happening in the tables you play.
The HUD is just a tool for you to track what all the players are doing. its up to you to interpret/analyse the stats and make your decision in the table.
Also, off table, you can use it to review and study your previous games to find leaks and mistakes you can fix the next time you get in a similar situation.
For HUD choice. Pokertracker,Holdem manager and DriveHUD.
I go for DriveHUD because its easier to use in the long run. Plus, their support team reply very fast compared to other database support I tried.