Kevin, in a way, they are apples and oranges, in other ways, they are the same car. I had a 1958 TR3A the same time my girlfriend had an early TR4. This was in 1966.
Performance is the same: they have the same crappy steering and rear suspension. The 4 has slightly more hp, but it is a little heavier. So, performance is a wash. "Sportiness" is a different kettle of fish: with the low doors and smaller "feel" to the car, it was no contest. The 3 was a true sportscar for us oldtimers, whereas the roll-up windows were heresy. As an eye-catcher, the 3 had it over the 4, also. I can't comment on the "ride feel," as it was so long ago and my butt was 50 years younger; but, neither of them rode like a Rolls Royce, but we did not expect them to.
Now, for driving convenience, mah jongg! No contest. In top-up weather, there was ALWAYS something coming up where you were thankful you had the roll-up windows, whether a squall, a dust storm, a farmer spraying something, a swarm of mosquitos, something dead, et al. The sidecurtains are in the trunk, and, by the time you stop and get them installed, ...
We didn't have the trouble with the 4's convertible top that one observer had, probably just dumb luck on my GF's part. Her top was much easier to install than my 3 top.
Note: I just bought a TR3B. It has the 87mm pistons, and I can tell that it is alot peppier than my TR3A and her TR4 were. A lot peppier. I seem to be faster on the take off than most of the TR6s in our club, but, of course, they will leave me top-end, when their 150(?) hp kicks in. I wish I had OD.