Myself, I don't use any "auto UV mapping" tools whatsoever. I find they always let me down.
Rather, I unwrap the model
manually.
I make copies of each part of the model (so as not to disturb the end product), separate the various sides and rotate them so that they have that more optimal 90 degree angle to the flat aspect of the texture file; then, I arrange and
proportionally (re) size them so that more "important parts" get larger areas of texture and less important or less visible ones get less space on the texture map. After I get everything on one large square texture (which I create with a large rectangle in "Locked" mode), I zoom in and take a screen shot of it. This becomes my texture image, which I can paint. But even before I do that, I can texture my model with it, and later assign the parts to a more developed version of that texture file.
and set up my own "plastic model flue" style guide, take a screen shot of it, and make my own texture guide. The way I set this guide up, I can anticipate panel lines and rivet lines and set it up so that when I'm in Photoshop or PaintShopPro, I can draw these lines "straight" through or across the various parts... then, when I assign the texture to the model, it works much better.
Note in this guide graphic for an aircraft fuselage, how I set up the "model flue" so that, when I draw a panel line that will circumvent the fuselage, I draw one vertical line on the graphic, and it will be sure to line up all the way around the model when I texture it. Other texture artists rotate parts in various ways to cram every part in to maximize space... but I find this counterproductive when getting alignments accurate.
If you're having stretching problems the culprit is usually that your surfaces are being covered by an area on your texture that is "viewed from a high angle off' rather than the optimal 90 degrees. Hard to describe in words, but that's what causes "stretching". You try to defeat that when creating your UV map by maximizing all the spaces, so they're as close to 90 degrees relative to the view as possible.