This is a highly personal choice, and dependent upon a number of factors from the prospective owner's perspective. There is no "right" or "wrong" answer.
Disclaimer: I'd like to have any of these cars in nice, original, low-mileage condition. I don't dislike any SC year or model. They are all desireable and collectible.
But, since I don't yet own any of the subject models, here are my priorities, and why I chose the way I did:
1st. = 1995 5-speed: The rarest of the SC models produced; which puts it at the top of my list. Also, the added attraction of the last year of production. Since I already own a reference-grade 1989 5-speed, I'd like to have the 1995 to "book-end" the production years. Also, since I already own a early model, a later model will be a nice contrast; interior, body style, etc. All this makes the 1995 5-speed a shoe-in for me.
2nd. = 1994 5-speed: The second rarest SC in production. Not the last year production, so it loses some interest from me on that point. But, since it also represents the later body style, it would still make a nice contrast to my 89. Still, not a 95, so points off in my book.
3rd. = 1990 35th. 5-speed: Since I already own an 89 and 90, another early body style holds less appeal for me. There are also no firm numbers stating how many 5-speeds were built (hearsay doesn't count), so that gives me a little heartburn, from a collector's standpoint. Also, the 35th. was basically a paint and trim appearance package; there were no performance differences from other 90 SC's. Also, and this is purely a personal preference, I'm not big on the overall look of the 35th. model. Something about the black/silver with black wheels just doesn't do it for me. Also not a big fan of the contrasting seat inserts; plus they're made from unobtainium if there is damage. All things being equal, I'd rather have a white, red, or titanium SC. I'd eventually like to have one of each year, all in 5-speed configuration. If a nice 35th. comes along, I'd jump on it. But if not, a "regular" 90 will do just fine.
As stated above, this is a personal choice, so everyone can differ. Don't bust my chops if my choices don't line up with yours : )
Cheers,
JD