0.5mm seems to be almost everyone's favorite. I've been experimenting with 0.3mm, but I will never abandon 0.5mm entirely.
The Rotring 600 and 800 may be the best-looking mechanical pencils on the market. I have a black 600 in 0.3mm, but I keep wishing they would make an 800 in that size too.
Most of my pencil use is for notetaking. I've found that I can take notes quickly by writing very small in non-cursive, although I'm not sure why that works so well for me.
When I used a 0.5mm I had to turn it regularly to avoid the thick lines produced by the worn side of the lead. With 0.3mm I no longer have to do that. It took some time to get used to how fragile it could be, but using a stronger lead (Pentel Ain Stein) and developing a lighter hand did the trick.
I favor the Rotring 800 because I generally carry a pencil with me, but the 600 is perfect when I'm in my own office. The only pencil that comes close, at least for me, is the Pentel Graph Gear 1000. That and the 600 are the most precise pencils I've ever used.
The only problem with the Graph Gear 1000 is that the lower body section is plastic and tends to break at the threads eventually. I recently ran across a guy who makes exact replacements for the lower body in aluminum and brass. I bought one of each on eBay. Not only do the fix the one weakness, they also improve the balance, which I've alway found to be a bit top-heavy. The brass replacement does a particularly nice job of shifting the point of balance down to the grip.
Oh I see, definitely a very efficient approach with the 0.3mm lead, the Graph Gear 1000 it's one of my favorites and pocket safe 😅, the clip is very functional, you can attach it to your pocket very easily, and surely will last longer with that plastic part replaced.
I haven't use Pentel Ain Stein lead, it's very hard to find high quality lead where I live haha, would you recommend it?.
My pencil use is for studying math, I'm about to start computer engineering so I'm studying a lot harder these days, using these pencils give me motivation and comfort definitely makes the experience enjoyable! haha.
Ain Stein lead is good for any purpose, but what it's best at it minimizing breakage. I use it in all my 0.3mm pencils.
If you aren't having problems with breaking leads you may want to try Pilot Neox. They are still harder than average to break and they are the smoothest writing leads I've ever used. You get both a better writing feel and a cleaner line with Neox.
Fortunately, all of the major companies make good quality leads these days. If you aren't having trouble with what you can get easily there's probably no reason to change.
In 0.5mm I generally use B grade leads. 0.3mm is enough finer that want at least B and I prefer 2B for a slightly darker line. I've tried some 4B, and it looked nice, but I go through the softer leads awfully fast.
We have a lot in common. I've been working as a software engineer for almost forty years. I do more consulting and architecture work these days, but I still write code almost every day. The field has changed just a bit since I started. :-)
I hope you enjoy college. I learned an awful lot from it, not all of it from classes. And I had a great time doing it. For what it's worth, I recommend not focusing entirely on your major. Take some classes outside of your field just because they sound interesting. Having a broader range of knowledge and, especially, a broader perspective on the world really pays off in the long run.