I'm building a laptop and I'm going to swap the internal HDD with an SSD, but since I have never used one, I do not know which is the best. I admit that I do not know much about SSDs and I do not know which ones produce less heat, are more reliable, etc. I am open to any and all suggestions.
Personally, I don't pay so much attention to brand name when it comes to this sort of thing. I tend to like to look at benchmarks and reviews to get an idea of how well an SSD should perform.
You don't give too much details on your build, so it's hard to recommend one specifically, but I've had great success with the Samsung evo SSDs. I put one these into what was a crappy 4 year old PC and overclocked the cpu. It still runs competitively with brand new mid range laptops today.
If you want a fast SSD at a competitive price point, I would look into the Samsung 850 evo. The 840 series is also still quite good if you need to bring down the price even more. It has a Max Sequential Read of 540 MB/s. This SSD will set you back a cool $100 for 250gb.
If you're willing to spend a bit more you could also go for a NVMe PCIe SSD, which have god like speeds (we're talking 3.2 GB/s sequential write and a random read/write that absolutely smokes hard drives out of the water). But a glorious PCIe SSD comes with an equally glorious price tag.
SSD produce heat that is not a concern. There is no friction, and even in HDD where there is friction the temperatures do not reach more than 60 deg celcius. The brand does not matter as long as you do not buy at some funny retailer. What matters are not even the speeds provided - those are the speeds for sequential read and write. Please notice, that the more important factor is the IOPS, which will influence the overall responsivness and loding times. The sequential read/write are important only when you transfer larger amounts of data (GBs). I am going to reccomend for SATA connection Samsung EVO 850 and ADATA 550 Premier Pro simply because I have experience with both and they perform just great. But by all means, choose your own. There is so much choice on the market of the SSD which are all great, that you'd have hard time going wrong :) Should it happen though, you'd have a m.2 connection interfaced over PCI-e (!) I absolutly reccomend the quite new and cheap (for the quality) Samsung 960 EVO M.2 2280 NVMe. It's a beast, and it'll provide you a pure joy of speed - it has 3200 MB/s read and 1500 MB/s write speed at top, and 330,000 IOPS for read and 300,000 IOPS for write, which is at worst three times more than conventional SATA SSDs.