I'm surprised no one has mentioned any media streamers. These are ideal if all of your content is stored on another networked computer or NAS, not to mention
Coming to the business end of the review, it must be quite clear by now that we can't recommend the GT 520 or the AMD 6450 with full confidence. They are probably doing well in the OEM market by getting incorporated into generic systems (not geared towards HTPC use). A discerning buyer building a HTPC system, having perused the various sections in this piece, would do well to avoid these two products.
Both AMD and NVIDIA GPUs suffer from a host of driver issues for the discerning HTPC user. Catalyst releases have been known to break GPU decoding in applications like VLC (something AMD has promised to fix in their next WHQL-certified driver). Supported refresh rates disappear from Catalyst if GPU scaling or ITC post processing is enabled. Different refresh rates default to different pixel formats on AMD cards. The HDMI audio driver maps the surround sounds in a 5.1 track to the rear surrounds in a 7.1 system on both NVIDIA and AMD cards. Both NVIDIA and AMD cards have been known to suffer from the silent stream bug at various points of time. Issues with RGB output levels and dithering resulting in banding artifacts on some displays have been reported on cards from both the vendors. The frustrating issue is that these problems get resolved in a particular driver release only to reappear in a later release. Unfortunately, issues like these are part and parcel of the HTPC experience. Both GPU vendors have a lot to learn from each other also.
If you prefer only AMD cards, the 6570 is the perfect HTPC card. The set of post processing options provided is very broad compared to what is provided by NVIDIA. All post processing options are enabled irrespective of ESVP, even for 60 fps videos. It has the highest HQV benchmark score of any HTPC-oriented GPU that we have evaluated so far. We didn't encounter any bitrate limitations with video playback. The pesky 23.976 Hz refresh rate may be a hit or miss depending on your setup, but it is way better than Intel's implementation. The lack of support for open source software developers and pricing relative to the NVIDIA GT 430 are probably the only complaints we can file against the 6570.
If you prefer only NVIDIA cards, the GT 430 is the perfect HTPC card for which you can obtain a passively cooled model. For enthusiasts, the ideal card would be one having more shaders than the GT 430 (for better madVR processing) and also the new VPU engine. However, there is no card fitting those criteria in the market right now. Our first impressions of the GT 430 last October were not favorable. However, driver updates have finally brought to fore the capabilities of the GPU. NVIDIA's support for the 3D ecosystem is better compared to AMD's. Support for custom refresh rates is a godsend for the videophiles and advanced HTPC users. The extensive support from open source applications is a definite plus. It is no wonder that most of the multimedia application developers swear by NVIDIA cards. The video bitrate limitations (not something one would encounter in real life), lack of comprehensive post processing options and the post-processing results when compared to the AMD 6570 (quite subjective) are probably the only complaints we can file against the GT 430.
If you are not in either camp, I would suggest going with the GT 430, if only for the price. Just last week, Newegg had a deal for the GT 430 at $20 after MIR. At that price, the card is simply unbeatable. At $70 without rebates, it is a more difficult decision to make. The 6570, retailing around $75, is probably a more future-proof card and has a better out-of-the-box HTPC experience. If you are the type of person who likes to constantly tinker with your HTPC and get excited by software tools which expose the HTPC capabilities of your GPU, go with the GT 430. If you are the install-it-and-forget-it type, a DDR3-based 6570 is the right card.