For me it was Battle Fever J, I prefer to start franchises from the oldest one I can find subtitled and that's the oldest I found.

My gateway drug believe it or not was Zyuranger. On accident! I was browsing the Netflix instant queue one Sunday mornin' and I noticed that MMPR was listed among the TV selections. Keep in mind I was 15/16 when MMPR originally aired. I read back in the day about how this was a show that had originally aired in Japan and this was a localization. I gave it a shot and to be honest I didn't care for it. Bulk and Skull didn't help. I liked the Zord and the fight sequences but that was it. Now, back to my original point. Sooooo I decided to give MMPR another shot and I watched the first ep. and was still underwhelmed. Maybe more so now given my current age. Out of curiosity and given my knowledge about how I had always known about MMPR being based off a show in Japan I decided to research on Google and find out what show this was based on. After a minute or two I found out that MMPR was based off of a show called " Kyōryū Sentai Zyuranger". I was like cool, let's see if I can find a sub of that show and make a comparison. I found a streaming site called Vimeo that had the first three eps. subbed. After seeing the original source material I was like WHAT THE FFFFFFUUUUUUUUUU......
No comparison at all. Best of all no Bulk and Skull!!! After that I stumbled upon Gokaiger and the rest is well...history. After keeping up with Gokaiger and watching the full Shinkenger run I'm a fan.

The first full Sentai season I watched was Goseiger. How I'm still a Sentai fan, nobody will ever know.

from the episodes that I watched, Goseiger wasn't THAT bad

Magi-Ranger. I saw the story, and just loved the family aspect of it. Been a fan ever since. Didn't get too much into, Go-Onger, though. What I saw of it, the story didn't appeal to me.

I use to watch clips on the internet back in 2000 when Timeranger was out. The first Super Sentai movie I seen was Gaoranger vs Super Sentai. Then I had some Gaoranger R2 DVDs but never finished the series. Dekaranger was the first series I've watched all the way through.

Dekaranger.
A Damn good place to start too!

My first Sentai series was Shinkenger, and boy did it leave a good impression. That, along with Power Rangers RPM being my first Power Rangers since I was less than 10 years old and Kamen Rider W being my first Kamen Rider series, left an excellent impression on me about Tokusatsu.

Now I recommend any starters to Sentai to start with Shinkenger, or, nowadays, Gokaiger. I still think Shinkenger would at least give them some bearings before starting on the crossover extravaganza of Gokaiger.

Not going to lie, it was Gokaiger, though I have sadly not continued it since Episode 6. Planning on continuing it though next month, that is, if I remember

WOW! I'd noticed a lot more Toku fans recently, I'd assumed they were just becoming more Vocal....guess thier just new (nothing wrong with that) First Sentai I ever saw was Megaranger, first watched in full was Hurricanger.