There's no standard method for measuring response time and distilling it down to one number that all manufacturers use, so it's basically meaningless, and even within the same brand, lower response times don't always look better in practice, especially if they have inverse ghosting. The contrast ratio is often "dynamic contrast", which is useless in practice, because instead of comparing white and black showing at the same time, they compare the luminance of an all-black screen with brightness set to minimum to that of an all-white screen with brightness set to maximum (the dynamic contrast is supposed to adjust automatically).
As for what to look for:
2. Panel type (viewing angles are a good indicator of this if it doesn't explicitly say which kind it is; 170/160 means a TN panel, which usually has low ghosting but weak color quality)
3. Glossy/matte panel (especially if using in a strongly lit room, but this can be hard to find)
4. Stereoscopic 3d capability (if you care about that)
5. Wall-mount or pivot capability if you care about that (the latter can often be provided by using a separate stand)
There might be other details to care about, but I don't remember any others at the moment.
I suggest you just get the VS238H-P, since it's less expensive.
I support your decision to use your own speakers. Monitor speakers are usually pathetic.