I've encountered some performance problems with a previous SSD so I would like to know what to look for to have a happier experience with my next drive
The four corners of SSD performance is: sequential read, sequential write, random read, random write. I would rank them in order of importance like this:
Random read is the most important since most of the IO in windows is random read, so the speed things load depends mostly on it, and then on sequential read. The ability to sustain good random write performance is a good sign that the SSD controller doesn't have any stuttering issues. Sequential write mainly matter for when copying files.
A problem is that for many SSDs the manufacturer and sellers only list sequential read and write performance so yuo have to look up random read and write performance from reviews online. A favorite source of mine is Anandtech.
The support for TRIM is also important, as well a good garbage collection. Support for TRIM is usually found in the specs, and a good review will test the garbage collection.
Another factor is reliability, which can be really hard to get good data on. Best I have is this:
This is the returns for SSDs for a French etailer, data from here.
There is also this: Choosing a Solid State Drive. It is from last summer so it is a bit out of date, but not much has happened in the SSD market except that there are more size options available for most models.