I own both a Squier Affinity and a MIM Standard Tele. When deciding between the two, a lot depends on your desire (and ability) to tinker with guitars. Do you want to buy a guitar as leave it as "it is," or do you have a hankerin' to swap out switches, pots, pickups, etc...
Affinitys make great modding platforms. The necks are a tiny bit narrower at the nut, and some can't stand this. Frankly, I don't notice it. I play a variety of electric and acoustic instruments (4, 5, 6 & 12 stringed), each with a different neck. I don't really register the difference in my mind or fingers. Some disagree (and you are welcome to). I like my Affinity neck quite a bit. I've done a lot of my first guitar mods on my Affinity (taking a router to the body to add a P-90, electronics swaps, etc...).
I got my 1995 MIM used (with a pretty good "relic job" on it) for $119 at GC! With the thicker body, it's got more heft than my Affinity and I love the way it looks and plays. The Fender neck had been played so much by its previous owner that it needs new frets. I wanted a cool 1960s Mike Bloomfield look, so I found a Squier rosewood neck, which it sports to this day. I may try to re-fret the stock maple neck myself one day.
I'm a tinkerer, so I've swapped pickups and electronics on both Teles over the years. I'm about to make an Esquire out of my Affinity (just for a change).
So, my thoughts... I strongly suggest looking for a USED guitar. You can get a LOT more bang for your buck (and more mojo, too). Also, a good compromise between the Affinity and the MIM Standard is the Squier Standard Tele: full body thickness, nicer pickups, string-through body. I sometimes wish I'd found the extra $40 to get one of these instead of my Affinity (I was hooked by the butterscotch blond finish, which I'm planning on painting over now).
Think about what features you "really" prize, then weigh how hard or easy it is to upgrade to them later. Swapping electronics? Easy. Vintage bridge? Harder (if you have to drill holes). String-through body? Harder still. Get the guitar which has the feature you like that are HARDEST to add later.
Also, as will doubtless be mentioned, play them (if you have the luxury of local music stores). Your guitar may "pick you" instead of the other way around. It happened to me once. If it happens, GET THAT GUITAR.
If I were NOT interested in upgrading anything, I'd probably look for a used MIM on Craigslist. They can usually be found for $250-$300. If I were a modder, it's a toss-up. The Affinity starts as a great low-price instrument. It can be turned into an awesome player (with some time and money).
Good luck on your quest!