Good question !
My ST collecting started about a year and a half ago.
I was going back to collecting after a 15 years break and knew I wanted to focus on Silver Age Marvels. Being a Kirby fan, I was quickly attracted to Strange Tales especially ST 101-109 since they had great covers, included early FF apparitions (that were much cheaper than the originals) and were not easy to find (a good thing if you want to manage your comic book collecting budget )
The first book I ever bought on eBay was a raw ST 106 for $80...that subsequently became a CGC 8.5 OWW A good Omen
At first I wanted to focus on FF apparitions only, but more and more I liked this title as it included some notable "first" :
ST 102 : 1st Wizard
ST 104 : 1st Trapster
ST 106 : 1st FF cover apparition outside of FF comic book (same date as ASM 1)
ST 110 : 1st Doctor Strange
ST 114 : 1st Captain America apparition since Golden Age
ST 116 : 1st Thing cross-over
ST 123 : 1st Thor cross-over
ST annual 2 : 1st Spider-man cross-over (and 4th overall apparition)
I then decided to eventually build an 8.5 run of ST 101-129 (the last good cover IMO) But then Rich (Korvac Saga) opened his vault and unleashed all his ST dupes that he hoarded in the last years...and I had no choice but to go up to ST 134
That being said, a lot of books are tough to find in high grade, since some collectors still hold on to them ( I don't blame them...well, maybe a little!)...but it only raises the thrill of the hunt.