Various factors explain why there is no easy way to do a rigorous quality comparison of NLEs.
Budtow presents a valid reason to be cautious and not experiment with multiple NLEs on a single system. Besides potential conflicts, each product leaves a big trail on a hard drive that can be messy to track or clean up. System performance can slow down too.
There is also a "learning curve" for any product, and few people will do a twin version of a project on two NLEs, from scratch to finish, to test the respective playback quality.
NLE reviews in most publications or sites are based on rather quick surveys by people who must write several reviews a week to earn their way. That entails far too little time to check out an NLE in detail. Another constraint is that any "expert review" is likely to harp on things that leave an average novice buyer cold, or might not see the forest for the trees.
Camcorderinfo provides some fairly objective comparisons of the quality of various models' video, using fixed tests. Too bad no site offers a similar comparison of the output of various NLE products.
Some playback software may present options to display some rigorous measure of bitrate, compression noise, and contrast ratio. This might help the analysis, but I've never seen a product-by-product analysis with this rigor.
One thing is certain: all the primary consumer NLEs offer similar prices for their basic products, then try to earn premiums through sales of plug-ins, updates, and add-ons. Another thing is nearly as certain: it's a tough business, and not very profitable in the current market. Avid and Corel are the only two public companies whose video software is a large enough component of their sales to gauge the segment profits (or lack thereof). Other companies are private (Nero, Cyberlink) and disclose no financial data, or else the video software product is only a tiny fraction of their business (Adobe, Apple, Sony). I'd bet that the consumer NLE segment profits have fallen or are in the red right now. Some firm's continue to post profits overall, albeit down, but that does not mean it is easy to get capital assigned to upgrade the NLEs or provide support.
Nero is the most versatile and economical product, but has the least depth, so far as video editing features go. The consumer versions of Premeir and Vegas offer some depth, but are hard to learn, lack convenient add-ons like Montage, and the forums and support are dominated by people who may know one element of videography well, but possibly never held a camera or burnt a disc. Ulead products are nice, but its parent Corel is the most financially distressed of any. Roxio sells some popular disc burning software, but (last time I checked) does not provide full support of AVCHD. Cyberlink's PD is a close competitor of Pinnacle Studio in many respects. Some say it is more stable, but I also read forum postings that observe image quality loss. One reason I'd not bother to switch to PD is that it offers no AVCHD smart render advantage relative to Studio. The reason Nero's smart render feature is not that attractive is that it works only when burning a disc, and the editing function and burning function launch separately. Files exported from the edit function are recoded, and the edit platform is very bare bones. People who say Nero loses less image quality can only be referring to burns of big clips which got no editing. Studio Ultimate has lots of add-ons and effects platforms which I admit I've only begun to experiment. One could spend a week to cook up a 1-minute super-dooper title sequence in Boris. The only big disappointment is that neither the built-in image stabilizer or the Mercalli version work as they should (no miracles, just some stabilization, please). No product I know of preserves native Dolby 5.1 sound, making 5-channel sound a somewhat useless export option.