Best 256GB SSD I can get for mid-2012 MacBook Pro

Best hands down in performance is the Samsung 840 Pro. The 840 Evo isn't as fast but it's cheaper.

I've got an 840 Pro in my 15" and an 830 in my 13", and they've never presented a problem. Just make sure to enable TRIM.

 

would depend on year and if its sata 2 or 3

 

The model year is in the thread title (2012), so he has SATA-3. Regarding 'best' it depends what you'd call best. I'd agree with the previous suggestion of the Samsung 840 Pro as one of the best.

Sandisk Extreme II is another one to consider, although I'm not sure how many people have installed those in a MacBook Pro, while the Samsung appears to be more popular. Review of the Sandisk Extreme II here:
http://www.anandtech.com/show/7006/sandisk-extreme-ii-review-480gb

 

If you're not on a budget, then the Samsung 840 Pro would be your best bet. Should you want something more affordable, I would get the Crucial M500.

 

Yes, I should mention I also ordered the Crucial M500, as I didn't feel the need to spend the extra $55 (current price difference compared to 840 pro on amazon.com).

 

Best SSD? Search in Google results;
http://reviews.cnet.com/8301-3132_7-57573094-98/top-5-solid-state-drives-its-upgrade-time/
http://www.tomshardware.com/reviews/ssd-recommendation-benchmark,3269.html
Many users on this forum have a preference for Samsung products, with perhaps Crucial the next in the popularity line, so you can get a lot of opinions on these drives here. Head over to anandtech.com for specific reviews on many different brands, (use the search function on the HP) such as Plextor, etc.: http://www.anandtech.com/show/6153/plextor-m5-pro-256gb-review

 

840 Pro. Hands down.

 

840 Pro is one of the fastest, but also 840 Evo should work really fine for every days work.