What's the difference between the two?
Pens are basically included batteries, you'll charge them individually. Mods you replace the batteries, which you can have sitting charging while you use what is in your setup.
Personally I've always liked the tube feel. I've recently purchased the Aspire CF Mod which is a 22mm diameter tube that I can toss in a 18650 battery, love the thing. But, depending your tank/topper you'll have different results. For me I love some of the tanks I have, I love some of the bigger box mods I have, but what is satisfying me the most right now is this Haze Dripper Tank on the CF mod, the single battery is enough power and the topper has one of the best flavors I've experienced, basically like a dripper but with more convenience because of the small tank below it that wicks up.
But, as others have said, what do you want, there's a whole spectrum of desires and builds. Some people want to replicate smoking a cigarette, that's basically MTL (mouth to lung) you kind of suck it into your mouth then inhale. For that there's a lot of options, personally I have custom built my TFV4 mini into a working option, but the best as I understand it are the Goblin Mini (if you want to build your own coils and are ok with a bit of a troublesome refill system) and the GS tank which you'll be buying premade coils for.
If you like DL, best flavor/price/overall is probably the Crown tank, but to get the full experience you need a 100watt device which means a mod, likely 2 batteries so a bit of a boxy feel.
Basically if you want a "this is what you want" answer you need to define your parameters. What do YOU want from your build?
Some people want the biggest clouds they can get, in that case you're going to want a dripper or a highend tank or more likely RTA. For Drippers there's TONS of options. For Tanks, you'll be looking at the TFV4, Crown, or possibly some of the newer ones like the Herekles Plus or Arctic V8. For RTAs (you'll have to rebuild the coils yourself and wick them) you'll be looking at something like the Bellus, Crius, or the newer Griffin/ VMCT(?may have forgotton the exact name on that, but it looks awesome).
Tons of options out there, again you need to better define what you want to get correct advice.
Do that and I'm sure you'll get plenty of help here, but the people here with the knowledge also know that the desires are subjective. If I were to give you an answer I'd say the Haze Dripper Tank with the CF Mod, but you may dislike that. Another person may say the Eleaf Istick 100w with the Crown tank. Another may say a parallel mech mod with a dripper... people's preferences vary.