I let em roll and if they don't like it, then they can have "the helping hand of the dm", where I re-roll and they get what it is. but only if I think they need a re-roll.
Well, in the game I am Playing in we start with Max at 1st level and then get 62.5% of the new Hit Die each time we go up. Save the fraction of a hit point and when it equals a full hit point it counts as a point.
In the game I Dm, start with 100% at 1st and then it goes down 10% each level until it hits 50% and stays at 50%. If the player wants to, at any level, they can Roll the die but they are stuck with what they get.
Or if they want they can do the 62.5% as above, they must choose what they want at creation and stay the path.
Killing the PCs is easy no matter how many HPs they have if that is what you want to do...But that is not what I am the DM for. It is my job to beat them down and make it tough but still fun for the players. YMMV
I've been using a certain method for over 20 years and that should tell you that I've been doing this too long. My method catches on with just about everyone I play with so it seems to have a certain appeal.
1st level- Max HP
2nd level and up Roll, decide to keep or take a GM re-roll.
If player opts for GM re-roll they get that number even if it was worse than the player generated number, this has the effect of shifting the HP curve slightly toward the upper end for Classes with a big die (D10-D12) and a bit more drastically for classes with low hit dies( D4-D6). I also use this method for healing magics, casters casting a healing spell can choose to have the healing re-rolled, but must accept the GM roll if they opt for it.
d4, roll = roll.
If you rol a d6, 1s count as 2s
If you rol a d8, 1s and 2s count as 3s
If you rol a d10, 1s, 2s and 3s count as 4s
If you rol a d12, 1s, 2s, 3s and 4s count as 5s