There are such good comments on both sides of this discussion that its clear there is no single 'correct' answer. Its whatever floats your boat (pun intended!). Like several said - try the slip, if you don't like it, buy a trailer.
I've thought about getting a slip but decided against it.
We live 1 hour from the nearest lake - Lake Conroe - and store our Bennington ten minutes from our house on its trailer in a $80/month fully enclosed and locked storage unit that is on the way to the lake. Ten minutes to hook up and we're on the way. Launching takes 30 minutes, half of which is wait time and parking the trailer at the end of the very large lot. (I've found that locked and covered storage is nice! I can put it away wet without the cover on, leave the seats and storage compartment open, and its nice and dry when I pick it up)
When my brother had the boat on a lift in his backyard, it took him at least 30 minutes to launch - taking off the playpen cover, loading up gear, bringing down coolers from the house, etc. Even longer to store it, because its harder to put the playpen cover on than take it off.
If I had a marina slip, I would have to carry all the stuff (coolers, life jackets, and the assorted gear I don't want stolen) the 1/4 mile from the parked truck to the slip, and then back again at the end of the day. When trailering, it goes from the back of the truck into the boat while we're waiting in line - 5 minutes (I have a very organized system of storage boxes categorized by: standard gear like life jackets, fishing gear, water toys etc - just take what I need for that day). Average ramp wait time on a busy weekend - less than 10 minutes.
Slips at Lake Conroe are $200/month. That's an average of $100 per launch vs $15 for the ramp fee.
Then there's the fact that I'm a DIY tinkerer.
Last weekend, I had the boat at the house and had a great time working on it - installed a fantastic flag pole from Taylor Made on the ski deck, fishing rod holders by Taco, a new anchor-light base from Perko (which included a lot of new wiring work), front bumper protectors I picked up from the dealer, plus some all-around cleaning and generally just enjoying being busy with my boat. Most of that would have been difficult to impossible at a marina slip (or at least, every time I dropped something it would have been gone for good!)
There's also the adventurer component. Having the trailer allows us to travel to new and different lakes. We love exploring - whether it be secluded coves or oogling expensive lake houses. So far we've ranged as far from Houston as Lake Ouachita in Arkansas and Lake Travis in Austin, and have plans for the Florida panhandle. Maybe someday further west. Lake Powell is a bucket list item.
Having the boat in a slip would result in us using it more only if it was in our backyard. Its not, so I'm not seeing a lot of advantage to that $200 cost.