I think it depends what you are using them for. also not sure if you are asking about my amps specifically, as they sit right here right now- how I like them, or those different models in general, apples to apples? The 66-J, for example, will need a full servicing and speaker job, or else I will have to get a different one if I want to keep it all orignal. It cannot meet its true potential the way it sits right now. I have heard 66Js in all their glory though...I dont think u could go wrong with any of the Guild amps I own. I think the Thunderstar/Superstar is the most easiest to find,and my Thunderstar is the smoothest sounding of all of them, if that makes sense. it also has 2 channels with 2 inputs each which is great if u have a pedal rig for the clean channel and a straight path for the reverb. they all sound similar in a way but different of course as well. the tremolo on the Mavereick and 98 RT is super surfy wavy. the trem is more "structured" on the Thunderstar. but the Thunderstar has never been worked on/recapped and the mav/98 RT have. not sure if that has anything to do with it. It (Thunderstar) does not sound like it needs any service or anything at all, it just has a different trem, more like a Fender tremolo/vib sound.
however if you want a small one the 66J is by far the smallest, just no reverb, and the stock speaker is low watts so not so good for pedals. The tweed Fender Tremolux is a 4 figure amp and it is said the 66-J and Ampeg Mercury basically sound just like it.
Each amp needs one or 2 little things and i hope to chip away at it in 2014 and see how good each of them can sound. so far they sound pretty good and I havnt done anything, so I'm pretty happy. There may actualy be one or 2 others on the radar, so like many others on this forum there may be some changes in the collection, we'll see. Space is becoming an issue so one or 2 guitars and/or amps will have to go, if i get any more new toys...or else aquire them with the intention of passing them on to someone interested here, or somewhere other than my apartment. I just couldnt pass any of these up!