Don't overlook the Sonitus effects. They're old, but so is a 1959 Les Paul

Sorry I mentioned True Pianos was a bad example as yes I have X3 Studio but my 8.5 is Producer. 
I find I have not even touched on what comes packaged with Sonar yet. I am not one to spend all day doing that. My needs are those of old school recording where you were lucky to have a good reverb, delay, compressor and EQ unit in a rack.. to me it's overwhelming if there are to many choices. I have not ventures past the tools on hand.
Only thing I do find interesting is soft synths that emulate traditional keyboards sounds. Mr Tramp is my only 3rd party plug in so far. The rest is all Cake and Steinberg.  

Thanks for all the suggestions.
 
Given that there are a half dozen options for classic effects (reverb, etc.) and many options for classic synth sounds, etc., I'm just hoping for a sorted list of what to choose assuming the latest is the best first-choice, without knowing what an older plug-in may have that the newer plug-in doesn't.
 
Perhaps the best thing is to spend some time familiarizing myself with the "tool-set" and make notes about each soft-synth and effect, and perhaps removing those that are redundant and older so the lists aren't so long.

Out of the included reverbs, I would probably go for BReverb 2 Sonar first, and for synth sounds, Z3TA+ although the initial bank of presets that opens is very dance oriented (and a little dated by now).

All of em.
All of em at once.
 
I did that after watching one of Craig Anderton's mixing vids. I used every one of his tricks in a single sound montage madness. useless. Worthless. Fun learning but ... yuck! haha

I am not sure if there really is a solution other than to "play around with each one." The advantage with soft synths is that you can replace them, so swapping around is pretty painless. As far as other features, the best way to learn is to play with them by creating things, read the forums, and if you come into a "snag" with something that isn't obvious to ask a question here.
 
The "preset" comments above are accurate... often the first impression of something is what we see through presets, but that may be only a small representation of true capabilities. Digging in further is the best way to understand things best.

I tend to install and use everything. I use Addictive drums for everything now. but I have older projects that have session drummer. If I ever need to open those projects again I will need session drummer installed to use it. I also installed the r-mix plug from S2 and the VC-64.
 
While I don't rely on the VC-64 as much for future projects. I have older ones that use the plug. that's why I put V-vocal on too. Melodyne is much better. TH2 is better than any previous guitar synth. Breverb is awesome too. I still like and use the Sonitus plugs.
 
To me the big improvements are in the pro channel. Those plugs are awesome. So I tend to use the newer plug- ins but I keep the older ones around for older projects that may be opened.

Here are my notes after going through all my installed synths. I post it here in case others have different opinions about my impressions:

• Session Drummer 3: Use Addictive Drums 2 instead (more powerful); use this for midi loops?
• Cakewalk Sound Center: Pretty good quality and variety of all types of samples/sounds. Simple program-specific effects (not customizable, but adjustable), Cakewalk sells expansion packs, not all samples are present in default version (e.g., most brass, etc.)
• Square I: [use z3ta+ instead] -- 3-oscillator standard synth (not just square waves); funky interface (manual may help?); old school synth sounds
• Roland Groove Synth: Old school (90s?) replica of sound box with standard patches... not likely useful
• Cakewalk TTS-1: Basic wav sample player with all standard midi instruments; use as later choice if patch isn't elsewhere; not much customization
• DropZone: Audio sample playback (.wav) with some modulation (pitch, cutoff, amp, looping), no effects... probably good for percussive effects?
• SFZ Player: Sound Font Player that plays sf2, wav and ogg files (old file types?)
• DreamStation: [not installed] -- looks similar to z3ta+
• Studio Instruments Drums: Use Addictive Drums 2, but the "SI" items do have common midi loops that likely work well together
• Studio Instruments Bass: Go-to bass guitar
• Studio Instruments Strings: 1ea Bass, Cello, Violin accompaniment, keyboard split between the 3. Effects and midi patterns available for quick work
• Studio Instruments Electric Piano: More variety than Lounge Lizard (Rhodes only), but not as much control. Also has many midi patterns matcing other "SI" instruments.
• Dimension LE: (Use Dimension Pro)
• Rapture LE: (use Rapture, not LE)
• Cyclone: Similar to RXP (loop sample player) but seems to allow more simultaneous loops and a large grid for selecting which part of the sample to play when. Probably similar to built-in matrix view in Sonar?
• Pentagon: [won't run] "Performance Oriented Synthesizer" looks like similar to z3ta+
• PSYN II: Similar to z3ta+? (classic synth with many controls) but with worse interface; may have unique presets
• RXP: Sample loop player with slicing and key assignments; plays rx2, wav files
• Z3TA+ Classic: Powerful classic synth with sounds modifiers (LFO, envelopes, etc.)
• XLN Audio Addictive Drums 1: (use AD 2)
• XLN Audio Addictive Drums 2: Should use as default drums, lots of kit samples, customizations, effects, midi patterns (be careful not to use Addictive Drums 1)
• AAS Lounge Lizard SONAR: Highly customizable rhodes e-piano, but not much else (can purchase other e-pianos). Better sounds when tweaking default presets.
• AAS Strum Acoustic SONAR: acoustic guitars only (nylon & steel), great strumming midi, non-standard keyboarding. Midi patterns available, effects
• Rapture: Wave-table synthesizer with advanced sound manipulation capabilities. Very much like Dimension Pro but more geared toward electronic sounds with more parameters; lots of FM
• Dimension Pro: Wave-table synthesizer with highly customizable (modulators, filters, etc.) with large library of samples, lots of fx, etc.  Can play REX (rx2) files (loops). Similar to Rapture but geared toward acoustic multi-samples. Should be default for acoustic sounds not found in dedicated synths.
• TruePianos Amber: Go-to for acoustic pianos
• Sample Tank: Clunky interface, but samples are nice. Use if other options are poor.

Sample Tank is not bundled with SONAR.
 
To run Pentagon, SONAR must be run as administrator.

jpaul
Square I: [use z3ta+ instead] -- 3-oscillator standard synth (not just square waves); funky interface (manual may help?); old school synth sounds

I would probably use Pentagon, it will run if installed correctly, in preference to Square as they are similar but Pentogon is more powerful and 64 bit.  Z3ta is a different beast all together. You will get sounds out of Square and Pentagon that you can't get from Z3ta and viceversa. Z3ta is more powerful for sure but Square/Pentagon are better for classic analog sounds.
The same applies to some of your other substitutions.