Spikes or Spikeless

You WANT the spikes to 'drill through' to the concrete. The key issue being even pressure downforce on all four spikes. You would need to find the right spot for sound from your speakers, Then check the spikes after forcing them completely through the carpet and pad to the concrete surface. and check the way they are balanced. If you have to add a bit of thin washer spacers on one or two spike then do it. (Even concrete floors are not usually perfectly flat) Keep at it until they all match in the weight they carry. When they all are balanced you will find the speaker really vibrates less. When i had B&W 805S on stands, getting the spike pressure balanced across the four spikes just right made a difference. The cabinet stopped vibrating! And the music sounded cleaner.
If you have adjustable spikes it is much easier, but even with non adjustable spike you have to add washers to it is well worth the effort.

PS: (even with four footed equipment with stiff chassis... to check those take a slip of paper and see how easily it pulls from each foot when in position. If one foot carries less weight that paper will pull out easier. add some thin paper shims under the foot (between the foot and chassis) until the feet all have the same 'slip' Then the chassis will vibrate less. and sound better.) a free tweak.

I have had good luck with spikes over concrete,with an area rug under the speakers and 1" thick Maple between rug and spikes..Spikes grip into Maple and are stable with the weight of the speakers holding everything down..The Maples is just cut 1" thick, 2"x 2" square under each spike.....

Speakers with four feet are a PITA. For all my previous speakers, I had custom Sound Anchor stands made, and those guys know the benefit of a three foot base. There is no need for the constant adjustment. My current speakers came with Sound Anchor bases the manufacturer has made for them and unfortunately they have 4 feet. Fortunately, they are easily adjustable and lock into place, but still I find the need to occasionally go back and readjust, maybe because the spikes are drilling into the concrete just a little over time under the over 100lb weight. If you have an option, and you can make the speakers stable with only three support points, IMO that is the way to go. As to your question, I have tried SA cone coasters, Audio Point cups and spiked directly into the floor on my carpet over concrete and I think spiked is best. On hardwood, I like coasters or cups with Herbies Big Fat Dots under them.

How heavy are your speakers? How thick is the padding and carpet? Have you tried your speakers with and without the spikes?

I also have a basement floor with carpet and padding. Over a 6 mo. to 1 yr. period I tried various combinations of spikes, wood plinths, rubber or composite footers, and nothing. This was for my VSA VR-4jrs. The worst was spikes directly through the carpet into the concrete. Grey, harsh sound with severely attenuated bass. What I finally settled on was a pair of custom maple platforms, 1" thick and about 2" extending beyond the speakers' plinths. Speakers spiked into the platforms, platforms spiked into the concrete thru the carpet. Got back my mid-bass, balanced out the rest of the spectrum, lost the harshness on top. I went with 4 feet on both sets of spikes but I have no doubt 3 would be better; also a 2" thick maple platform would probably be superior too. The platforms elevated my speakers a bit but luckily this did not cause problems re tweeter height and so forth.