Anything I've read suggests that giving them a chance to self regulate is best and reduces injuries from crowding each other to death.
The heat source of a lamp or heating panel let's the hot chicks move away from the heat and cool off and the cold chicks will move into the warmer area.
Recently read a post suggesting to put the modern overhead brooder panel on an angle, two legs longer than the other pair which allows for a similar self regulating choice of body temp.
Also to note were number of chicks per heart source. Better too many options than too little.
Do what it takes to avoid overcrowding as they'll suffocate each other. You watch to see if they are crowding close to the heat source or trying to escape it and adjust accordingly.
A lamp or two on a chain overhead is easily adjusted daily as they grow as well... Mixed hatches may grow at different rates so two lamps at different heights help with this as well.
I don't have any flock yet, but I picked up a heat lamp as my first piece of chicken kit. Plus side, they're cheap and plentiful, red bulbs help reduce pecking wounds. Buy non-teflon coated bulbs for your heart lamps as they off-gas and it's toxic (that's news to me but I read it on a post here recently). Always keep a couple of spares in the room with the brooder handy (they least for years but they are impossible to find when you need in a hurry).
Ooooh! And try not to approach your young flock from above like a predator would. You could scare them into a stampede that'll cause injuries. Put your hand into the brooder from the side and then move slowly towards the chicks, it's less stressful.
Hope this was helpful, it's all stiff I've read posted on here or in the books I have read on keeping chickens. Yeah I was geeking out and taking notes. Lol
Matt