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Hi kjcramer, welcome to NEX-land!
For legacy manual lenses, I've used cheap ($10-ish) Chinese ones for Minolta MD, Canon FD, Olympus OM etc and they've all been fine. I've read about occasional bad experiences with both cheap and expensive adapters. Standard adapters are usually "dumb" mechanical spacers for correcting the registration distance and providing a lens mount (a few also provide focusing or aperture control for lenses that don't have it manually available e.g. Contax-G).
Most of the old 50/1.4 and 50/1.7 options were typically pretty great - my MC Rokkor-x PG 50/1.4, Canon FD 50/1.4, Olympus "made in Japan" 50/1.8, Yashica ML 50/1.7 all are. With fast fifties and similar it comes down to preferences in rendering style/colour/bokeh, wide open performance, size/weight, price etc. Search this forum and Flickr.
APS-C-cropped 50mm (== 75mm) can be a bit tight for group/social/"normal" stuff etc, so you might want to consider a wider 28/30/35mm, but of course these won't be typically as fast, unless you pay more... I can recommend the great FD 35/2 (the 2.8 is allegedly as good & cheaper of course), FD 28/2.8, Vivitar Close Focus 28/2, Rokkor 28/3.5.
And for tele I use a great FD 100/2.8, Rokkor 135/3.5, Vivitar 80-200/4.5.
Also consider a Speed Booster or Lens Turbo focal reducer which, instead of cropping, optically shrinks down most of the lens's original field of view to APS-C size, gaining a little sharpness and a stop of light (in shutter speed, but not DoF) into the bargain, but risking blue-spot flare reflections in certain light and curvature/barrel distortion in the case of my Zhongyi FD Lens Turbo. So your 50mm becomes around 51/52mm, instead of 75mm-equivalent crop etc.
Sigma do razor sharp auto-focus plastic fantastic e-mount 19/2.8, 30/2.8 & 60/2.8, and the "native" Sony E-mount 35/1.8 & 50/1.8 are both great from what I've seen.
And search this inc. bookmarks bottom right for lots of great info/discussion: http://www.dpreview.com/forums/1042
Others will have other opinions and suggestions!