I've done both. I'm bad a stroke counting---I get focussed on technique and loose count. So, more often I use duration to approximate a rep distance (40s = 50scy, 1:20 = 100scy, etc).

I think I mentioned in your other thread that I use markers on the floor of the pool to indicate intensity. I just space them out every couple of feet-ish. So, the red fishy might be hard-50s, and the blue fishy might be easy-100s. fitness/technique improvement is then measured in fish-color x rep. Ie, maybe this week I can to 20x"50" to the red-fishy. Next week, I make it half-way to the orange fishy for 20x"50". But, maybe you like dolphins, or whales.

I've been using a Finis Tempo trainer and counting strokes. I set it to mode 3 at various rates. My racing stroke rate is around 85-90, so I start at easier rates and work to faster ones. My normal stroke count in a 25y pool is 19-21 so I have been counting 100s as 100 strokes figuring there are no flip turns. Maybe it is closer to 95 strokes but 100 is a nicer number. Anyhow, a sample set would be: 400 strokes with the Tempo Trainer set to 70, 2 x 300 strokes set to 75, 3 x 200 strokes set to 80 and 4 x 100 strokes set to 85. My tether has two ankle bands rather than being tethered at the waist. I like vertical kicking, particularly breaststroke as there is resistance as you kick down, then the feet fly back up to the butt as the tether pulls them up. I actually plan on adding some to our HS swimming bid list for our breaststrokers/IMers.

-leh