Hi, I’m going to be applying to Penn ED this year and I was wondering whether a transcript of equally divided A’s and B’s in a competitive public school (taking only Honors and AP classes all 4 years) would be a deal breaker in admissions, even if I have outstanding extra curricular leadership positions and decent recommendations, as well as a decent essay? Oh, also my standardized test scores are pretty good too. Do they truly take a holistic approach or would my application be thrown out because of my relatively low GPA?
A approximate 3.5 GPA is not competitive in the Penn admissions pool. There will be 1000s of applicants with strong ECs but +3.8GPAs in equally stringent curricula . It sounds like you’ll be prepared for college’s rigors (which is a great thing) but the competition at Penn and like schools is simply mind boggling.
I’m sure it’s changed since I applied ten years ago, but I had a mix of As and Bs in high school, with a C+ thrown in there sophomore year. My unweighted, core GPA was somewhere in the 3.2 range, and my weighted, reported GPA was a 3.9. I got in without being deferred.
If your application package is strong enough, I think you can get in with a pedestrian (by Penn’s standards) GPA. It will probably take a much stronger overall package with a mix of As and Bs than it would if you had mostly As. ED has a higher admit rate than RD, though that may be due to self-selection among applicants more than it actually being easier to get in.
As with anyone applying to a top tier school, my advice is to go in thinking that you will not get in. Give it your best shot, and if you get admitted, great.
It’s impossible for anyone here to tell you what Penn will think of your application. The best you can do at this time is apply and hope for the best. My guess is that most students are in the 3.8-4.0 range for unweighted GPA. However, a large percentage of students will be closer to 4.0 than 3.8 with a very difficult curriculum. However, I am sure Penn does accept students with lower GPAs. My advice to you is to try your best to highlight your best attributes and show why you in PARTICULAR would be a great candidate for a Penn education. Also, if there are any circumstances (such as sickness or death in the family) that impacted your GPA, make sure this is made clear in your application. I’m a firm believer that people should apply where they want to. It’s better to live without regrets. However, if you have concerns about the competitiveness of your application, I would advise that you also find some mid range schools that you love and don’t solely focus on Penn. Actually, I think that is good advice for any student, regardless of the strength of their application.
They will take a holistic approach, and while GPA is crucially important, a 3.5 isn’t bad. If the other areas of your application are strong, a [relatively] low GPA will not solely eliminate you as a candidate for admission. Just try your best! 
They definitely take a holistic approach, but gpa is a very important factor. As you can see in the CDS, 92% of students had a high school gpa that was 3.75 +, and the average high school gpa was 3.93. Link below.
That suggests to me that student who were was admitted with a 3.5 gpa know why. Maybe an athlete, a special talent, an extraordinary achievement, or that one essay that made the entire Adcom break down in tears.
I don’t know whether you will get in, an I definitely encourage you to try, but it is clearly a reach.
http://www.upenn.edu/ir/Common%20Data%20Set/UPenn%20Common%20Data%20Set%202015-16.pdf
In theory, some students get admitted with a 3.5GPA. Like Much2Learn says, you’ve got to figure what about those students made them wanted by Penn – what hooks did they possess.
For the unhooked 3.5 GPA applicants, probably 99% of them were rejected. Perhaps this miniscule percentage falls under @tmck2011 's definition of “not bad”
It doesn’t match my definition of “not bad”
OP: since you go to a “competitive HS” I assume it has history of successfully sending kids to selective colleges. Ignore all this CC noise. See what your counselors say. Perhaps your school has naviance. Perhaps there’s something in your profile that’s not obvious. To me, practically no one with a 3.5GPA should be thinking of applying to schools with admit rates in the teens. But that’s just my “noise”. Your GCs will know where to guide you.