If iI had a chance to choose like this, iI would probably want to be a Formula 1 driver or a Formula 1 race engineer.

"I" is always capitalised as a word on its own (also in forms like I'm)

The main reasonfactor that affects this decision is surely the major increase in my interest in motorsports recently.

"Surely" is a bit unnatural here.

"Factor" sounds more natural than "reason" here.

I'm stuck between these two choices because iI'm a little unsure of myself i, I believe.

"I believe" is sort of its own clause here, so more natural to separate it with a comma

I can't make a guess which one iI would love most due to ias I've never experience bothd either of them.

You could also say "make a guess as to which" but that's a lot more words so better to go with the simpler option here.

We tend to use "either" in negative sentences rather than "both". Could also use "neither", but then you'd have to remove "never" as neither already has the negative built in.

But the engineering part of this career would be a little more suitable for my current lifestyle.

It's an unbelievabley cool job.

The unbelievably is being used here to modify the adjective "cool" so more natural to use the adverb form.

"unbelievably" as a strengthener is so common that if you wanted to have "unbelievable" as its own modifier for "job" you'd have to "unbelievable, cool job"

Both of the engineering part and the racing driver part of the careerfield.

Engineering and racing are separate careers, so field works a bit better here as a more general, encompassing term.

YourThe prestige and the uniqueness of yourthe job makes this choice mucheven more perfect.

"even more perfect" is more natural than "much more perfect"

Not sure why this sentence went to second person randomly, so moved it to a more passive term to fit the rest of the post.

If iI had the chance to choose like this, iI would probably want to be a Formula 1 driver or a Formula 1 race engineer.

The main reason that affectsfor this decision is surely the major increase in my interest in motorsports recently.

I am stuck between these two choices because iI'm a little unsure of myself i, I believe.

I can't make a guess for which one iI would love mostprefer, due to i'vehaving never experience bothd either of them.

It's an unbelievabley cool job.

Both of the engineer part, and the racing driver part of the career.

YourThe prestige and the uniqueness of yourthis job makes this choice much more perfect.

I am stuck between these two choices because i'm a little unsure of myself, i believe so.

I can't make a guess which one i would love the most due to the reason that i've never experienced both of them.

If iI had the chance to choose like thiswho I want to be, iI would probably want to be a Formula 1 driver or a Formula 1 racecar engineer.

"like this" -> "who I want to be", Maybe makes the sentence more specific on your intention/goal/reason.

The main reason that affects this decision is surely thedue to my major increase in my interest in motorsports recently.

I modified yours, but it may sound unnatural. You are directly translating. But it is OK too. If it were me, I would say...

"The main reason why I want to become like this is because of my increasing interest in motorsports recently."

I'm stuck in between these two choices because iI'm a little unsure of myself i, I believe.

or "I think". But "I believe" is great.

I can't make a guess which one iI would love most due to ire because I've never experience both of them.

It is okay to use contractions. But if you are writing formal sentences you should not use contractions.

Example: "I've" -> "I have"

But the engineer part of this career would be a little more suitable for my current lifestyle.

Seems ok.

It's an unbelievdeniabley cool job.

undeniably = without a doubt

Both of the engineer part and the racingecar driver part of the career.

Seems ok.

YourThe prestige and the uniqueness of yourthat comes from this job makes thise choice much more perfect.